no article in october and November

For DECEMber 2002 issue

SCIENCE IN CRIME DETECTION-111

THE LATEST IN FINGERPRINTING: WHAT IS LIVE SCAN TECHNOLOGY?

‑Dr. Anil Aggrawal

Through this column we strive to give the latest in crime fighting technology to our readers. This time I am going to talk about live scan technology, which is the latest in fingerprinting. Let us see, what it is.

But first of all, some preliminaries. To start with let me ask you, what is an inked fingerprint? This question is a very important part of understanding how most fingerprint identifications are made, and how fingerprint files and databases are created. Essentially, an inked fingerprint is an impression of friction skin made with a medium such as printer’s ink. Ink is applied to the top surface of the friction ridges on the last joint of the finger, the entire palmar surface, or soles of the feet. These inked fingerprints can also be known as exemplar prints. Exemplar prints are those prints from a known origin or source. However, the person’s true identity may not always be known without further investigation. Exemplar prints are intentionally recorded friction skin impressions from a known person. Again, the term fingerprint is an all encompassing term and could be in reference to any area of the palmar surface or even soles of the feet which are called the plantar surfaces.

The term inked, as in “inked fingerprint”, is also a generality. A black printer type of ink has long been the standard medium used for recording friction ridge skin impressions. However, it is not the only means of making an exemplar impression. A computer-generated fingerprint image, often termed live-scan, offers a considerable speed advantage when compared to standard ink-type methods. It is common to record up to four fingerprint documents of an individual at a single printing event. Three of the documents may consist of duplicate l0-print cards destined for comparison and filing with local, state, and national government agencies. The court system may also receive documents with inked fingerprints.

Live-scan-type fingerprint imaging systems are used to electronically scan fingerprints. These images can then be printed to l0-print cards via a computer laser printer. Current laser printer systems used for fingerprint reproduction print in the range of 300 to 500 dpi resolution.

A word about dpi here. Dpi stands for “Dots per inch”. All printed matter is made up of dots. The higher the number of dots are, the better the picture. Do a simple experiment. See an ordinary newspaper under a strong hand lens. Particularly try to see a photograph. You will see a number of black and white dots. These dots make up the photograph. An ordinary newspaper has lesser number of such dots per inch. That is why its photographs appear more “grainy”. If you try to see a glossy magazine under such a hand lens, you may not be able to see, these dots. The reason is that these dots are much smaller in glossy magazines. That is why the pictures appear more glossy.

If we talk about 300 dpi, we are talking about a picture, in which every inch has got 300 dots. A 500 dpi picture has 500 dots per inch. These are fairly high resolution photographs, and would appear less “grainy” to the eye, than, say, a picture with 72 dots per inch.

Not all electronic images, or image output are defined in dot per inch resolutions. Thus, printed resolutions may vary. Dye sublimation printers, for example, print in “ppi” or pixels per inch. Also, the capture resolution of a fingerprint image also affects the output resolution.

With live-scan, the fingerprint scanning process is done only once, and duplicate 10-print cards can be printed as needed. Live-scan systems are fast-becoming the system of choice at larger agencies.

Another form of inked fingerprints, albeit nonstandard, may include elimination fingerprints in the form of purposely made and developed latent print impressions. This is an alternate method of recording victim elimination fingerprints when ink is not available. Field officers or a fingerprint specialist will have subjects press their fingers onto a white card stock. This transfers oils and moisture residues from the fingers to the blank card. Then a contrasting color of fingerprint development powder is applied to the card to develop the fingerprints. The card is then labeled with basic case and fingerprint information. Clear tape is applied over the impressions to prevent smearing of the delicate residues. This system works because the powdering is done immediately after the impressions are made. The moisture and oils contained in the fingerprint residues have not had time to evaporate or soak into the card stock. Properly made elimination prints of this type can offer quality similar to regular inked fingerprints. These elimination prints can then be used in comparisons just as inked fingerprints would, although, here the fingerprint record would not be durable enough to withstand entry into a file system and is almost always filed with the latent fingerprint evidence.

Major case prints, or major criminal prints, are recorded impressions that represent all areas of friction skin on the palmar, and if necessary, plantar surface of the feet. Major case prints are recorded in addition to the standardized l0-print and palm print cards. The very tips of the fingers, sides of the fingers, and sides of the palms are not always represented in normal printing of fingers and palms. Recovered crime-scene print impressions may be from one of these areas; thus, major case prints are needed before a comparison can take place. All fingerprint impressions represent only a fragment of a whole. Here, a whole print would be the three-dimensional palmar surface of a hand. Generally, most all ink and developed latent print impressions are two-dimensional fragments of a particular sample of friction skin. Major case prints are a collection of overlapping areas of inked friction skin impressions. The only way to record a complete palm impression is to make a three-dimensional mold of the palmar surface. The same is true regarding just the last joint of each finger; the patterned area of a finger, it is still not possible to record a complete impression at one time using standard inking practices. Even if the finger is rolled from one side to the other, the tip of the finger will not be represented because our receiving medium, a l0-print card, is a two-dimensional object.

In a detailed report of a comparison of inked fingerprints, one would expect precision in describing the exact area or areas that were compared. An example would be: Inked fingerprint card from Ram Lal was compared with known prints of Shyam Lal ID#123456 with date of birth 16 July 1974. A subsequent conclusion of identification or no identification would follow. Exacting descriptors allows the prints in question to be verified and/or inspected by involved parties.

Clerical errors can occasionally be made that allow inaccurate information, in all or part, to accompanying the inked fingerprints. l0-print fingerprint cards contain areas of information that are intended to be filled out at time of printing. Name, date of birth, date of printing, addresses, name of printer, and the fingerprints themselves each need to be accurately recorded.

LIVE-SCAN TECHNOLOGY

Having understood what inked fingerprints are, we can now turn to live scan technology. Live-scan is the computerized equivalent of inked fingerprints. A person’s fingerprints are scanned via a glass mirror reflection and electronic camera, or by such new technology as ferroelectric infrared thermal imaging. There are several different imaging solutions available. With the exception of the reflection mirror live-scan, most of the technology is relatively new and nonstandardized. The ferroelectric infrared thermal contrast system is being developed by the Thomson-CSF company.

The information from the fingerprint scans are converted into a digital computer code. Once the 10 fingerprint images are captured, the user can print out duplicate l0-print fingerprint cards on a high-resolution laser printer. Current live-scan technology resides at 300-500 dpi image resolution.

We have already talked about dpi resolutions. A 500 dpi is sufficient to reproduce some of the pores that line the tops of the frictions ridges. The lower 300 dpi systems cannot reproduce the pore or ridge edge detail reliably, yet it is sufficient for basic fingerprint identification when the live-scan machines are properly maintained and operated.

A live-scan generated l0-print card is similar in appearance to a regular inked card. The differences may include the addition of computer code added to the margin of the card. A gray scale bar and a laser printed operator’s name in lieu of a signature may also be present. Since all machines require a user specific password to access the imaging program, this has not proven to be a problem. This lack of hand written data also increases the accuracy of the data itself by not breaking the electronic chain of combining the fingerprint image data and the personal data during the printing process. Of course, agencies will have to supervise the use of the machine to ensure that other operators do not use the same passwords and log-on name.

In large agencies, live-scan electronic images are slowly replacing ink as the primary means of creating a fingerprint record. While ink requires that each finger is inked prior to each impression, live-scan allows each finger to be scanned as repeatedly as necessary to generate a clear fingerprint impression, but the best detailed image need only be captured once. The term capture of a fingerprint is that the image is digitally acquired for further processing and subsequent printing.

In general, novice, live-scan, computerized systems operators can produce clearer overall impressions when compared to using ink. Clearer images are the result of the fact that a live-scan operator has no reason to accept and capture a smudged image. While live-scan type print impressions generally result in a clearer overall fingerprint impression database, most fingerprint specialists prefer properly made ink impressions for comparison purposes. Ink allows great detail, if properly done. The problem results from the fact that unsupervised and/or undertrained fingerprint technicians in jail booking areas or public fingerprint counters will often produce a higher percentage of smudged fingerprints using the ink method.

The print can be rerolled until a satisfactory image has been made. Once this is achieved, the operator will move on to the next finger until all 10 fingers are rolled on the glass platen, then the plain impressions of each four fingers and thumbs are made along the lower part of the l0-print card. These nonrolled plain impressions will help ensure that the 10 fingers were rolled correctly. This procedure has not changed from the ink process. The fact that it is much easier to reroll fingers with the live-scan systems seems to generate better overall impressions with novice operators as well. Clearer l0-print cards equal a better database and an improved match, or hit rate, on subsequent database searches.

ARE THERE ANY DISADVANTAGES TOO

The system is not without its disadvantages. The main disadvantages of the live-scan systems are that most are not portable and require high maintenance. The systems and printers must be calibrated often to produce quality fingerprint impressions. Computer-generated artifacts can also be added to a fingerprint impression by the operator, the system software, or by the computer printer. User errors can result in the fingerprint of one individual being added to the information and name of another. These instances are rare they are not unique to live-scan hardware as they can also be found with the traditional ink method.

One of the main reasons for errors with computer-based systems may be because the operator may not always know what data the computer is currently processing. A I0-print card could be fed into a printer which is printing a different individual’s fingerprints. Most systems attempt to avoid this problem by eliminating as much handwritten data as possible by keeping the alpha-numeric data and the fingerprint images together throughout the printing process. A similar problem was noted with standard inked l0-print cards. If the descriptor data, such as name and date of birth, was not added to the fingerprint cards immediately after the printing of a person, it was possible that the wrong information could be added. With current systems, the main problems reside with the reprinting of data from electronic storage buffers, or the printing of miscellaneous l0-print cards that are provided by the customers.

The most notorious drawback of computer-generated fingerprints is not from the occasional error but an inability to reproduce very fine fingerprint detail. Computer-generated images often lack the nuances of a rolled ink fingerprint. These fine details or nuances are often used to compare fingerprints. So the trade-off seems to be that while computer-generated fingerprint images save time and can enhance the computer database’s hit ratio, they can also prove difficult for use in some of the more challenging fingerprint comparisons. The comparison of crime scene latent fingerprint impressions often rely on the fine fingerprint ridge detail.

Generally, exemplar and latent fingerprint impression quality is highly variable. As was mentioned earlier, it is not that uncommon to see crime scene latent fingerprints that are of a higher quality than the exemplar prints on file. Whether the exemplar fingerprint impressions are ink or computer-generated, the actual quality and detail of the print will determine its usefulness in comparisons.

This article has (2239) words

Dr. Anil Aggrawal, M.D.

Professor of Forensic Medicine

Maulana Azad Medical College

New Delhi‑110002no article in october and November

For DECEMber 2002 issue

SCIENCE IN CRIME DETECTION-111

THE LATEST IN FINGERPRINTING: WHAT IS LIVE SCAN TECHNOLOGY?

‑Dr. Anil Aggrawal

Through this column we strive to give the latest in crime fighting technology to our readers. This time I am going to talk about live scan technology, which is the latest in fingerprinting. Let us see, what it is.

But first of all, some preliminaries. To start with let me ask you, what is an inked fingerprint? This question is a very important part of understanding how most fingerprint identifications are made, and how fingerprint files and databases are created. Essentially, an inked fingerprint is an impression of friction skin made with a medium such as printer’s ink. Ink is applied to the top surface of the friction ridges on the last joint of the finger, the entire palmar surface, or soles of the feet. These inked fingerprints can also be known as exemplar prints. Exemplar prints are those prints from a known origin or source. However, the person’s true identity may not always be known without further investigation. Exemplar prints are intentionally recorded friction skin impressions from a known person. Again, the term fingerprint is an all encompassing term and could be in reference to any area of the palmar surface or even soles of the feet which are called the plantar surfaces.

The term inked, as in “inked fingerprint”, is also a generality. A black printer type of ink has long been the standard medium used for recording friction ridge skin impressions. However, it is not the only means of making an exemplar impression. A computer-generated fingerprint image, often termed live-scan, offers a considerable speed advantage when compared to standard ink-type methods. It is common to record up to four fingerprint documents of an individual at a single printing event. Three of the documents may consist of duplicate l0-print cards destined for comparison and filing with local, state, and national government agencies. The court system may also receive documents with inked fingerprints.

Live-scan-type fingerprint imaging systems are used to electronically scan fingerprints. These images can then be printed to l0-print cards via a computer laser printer. Current laser printer systems used for fingerprint reproduction print in the range of 300 to 500 dpi resolution.

A word about dpi here. Dpi stands for “Dots per inch”. All printed matter is made up of dots. The higher the number of dots are, the better the picture. Do a simple experiment. See an ordinary newspaper under a strong hand lens. Particularly try to see a photograph. You will see a number of black and white dots. These dots make up the photograph. An ordinary newspaper has lesser number of such dots per inch. That is why its photographs appear more “grainy”. If you try to see a glossy magazine under such a hand lens, you may not be able to see, these dots. The reason is that these dots are much smaller in glossy magazines. That is why the pictures appear more glossy.

If we talk about 300 dpi, we are talking about a picture, in which every inch has got 300 dots. A 500 dpi picture has 500 dots per inch. These are fairly high resolution photographs, and would appear less “grainy” to the eye, than, say, a picture with 72 dots per inch.

Not all electronic images, or image output are defined in dot per inch resolutions. Thus, printed resolutions may vary. Dye sublimation printers, for example, print in “ppi” or pixels per inch. Also, the capture resolution of a fingerprint image also affects the output resolution.

With live-scan, the fingerprint scanning process is done only once, and duplicate 10-print cards can be printed as needed. Live-scan systems are fast-becoming the system of choice at larger agencies.

Another form of inked fingerprints, albeit nonstandard, may include elimination fingerprints in the form of purposely made and developed latent print impressions. This is an alternate method of recording victim elimination fingerprints when ink is not available. Field officers or a fingerprint specialist will have subjects press their fingers onto a white card stock. This transfers oils and moisture residues from the fingers to the blank card. Then a contrasting color of fingerprint development powder is applied to the card to develop the fingerprints. The card is then labeled with basic case and fingerprint information. Clear tape is applied over the impressions to prevent smearing of the delicate residues. This system works because the powdering is done immediately after the impressions are made. The moisture and oils contained in the fingerprint residues have not had time to evaporate or soak into the card stock. Properly made elimination prints of this type can offer quality similar to regular inked fingerprints. These elimination prints can then be used in comparisons just as inked fingerprints would, although, here the fingerprint record would not be durable enough to withstand entry into a file system and is almost always filed with the latent fingerprint evidence.

Major case prints, or major criminal prints, are recorded impressions that represent all areas of friction skin on the palmar, and if necessary, plantar surface of the feet. Major case prints are recorded in addition to the standardized l0-print and palm print cards. The very tips of the fingers, sides of the fingers, and sides of the palms are not always represented in normal printing of fingers and palms. Recovered crime-scene print impressions may be from one of these areas; thus, major case prints are needed before a comparison can take place. All fingerprint impressions represent only a fragment of a whole. Here, a whole print would be the three-dimensional palmar surface of a hand. Generally, most all ink and developed latent print impressions are two-dimensional fragments of a particular sample of friction skin. Major case prints are a collection of overlapping areas of inked friction skin impressions. The only way to record a complete palm impression is to make a three-dimensional mold of the palmar surface. The same is true regarding just the last joint of each finger; the patterned area of a finger, it is still not possible to record a complete impression at one time using standard inking practices. Even if the finger is rolled from one side to the other, the tip of the finger will not be represented because our receiving medium, a l0-print card, is a two-dimensional object.

In a detailed report of a comparison of inked fingerprints, one would expect precision in describing the exact area or areas that were compared. An example would be: Inked fingerprint card from Ram Lal was compared with known prints of Shyam Lal ID#123456 with date of birth 16 July 1974. A subsequent conclusion of identification or no identification would follow. Exacting descriptors allows the prints in question to be verified and/or inspected by involved parties.

Clerical errors can occasionally be made that allow inaccurate information, in all or part, to accompanying the inked fingerprints. l0-print fingerprint cards contain areas of information that are intended to be filled out at time of printing. Name, date of birth, date of printing, addresses, name of printer, and the fingerprints themselves each need to be accurately recorded.

LIVE-SCAN TECHNOLOGY

Having understood what inked fingerprints are, we can now turn to live scan technology. Live-scan is the computerized equivalent of inked fingerprints. A person’s fingerprints are scanned via a glass mirror reflection and electronic camera, or by such new technology as ferroelectric infrared thermal imaging. There are several different imaging solutions available. With the exception of the reflection mirror live-scan, most of the technology is relatively new and nonstandardized. The ferroelectric infrared thermal contrast system is being developed by the Thomson-CSF company.

The information from the fingerprint scans are converted into a digital computer code. Once the 10 fingerprint images are captured, the user can print out duplicate l0-print fingerprint cards on a high-resolution laser printer. Current live-scan technology resides at 300-500 dpi image resolution.

We have already talked about dpi resolutions. A 500 dpi is sufficient to reproduce some of the pores that line the tops of the frictions ridges. The lower 300 dpi systems cannot reproduce the pore or ridge edge detail reliably, yet it is sufficient for basic fingerprint identification when the live-scan machines are properly maintained and operated.

A live-scan generated l0-print card is similar in appearance to a regular inked card. The differences may include the addition of computer code added to the margin of the card. A gray scale bar and a laser printed operator’s name in lieu of a signature may also be present. Since all machines require a user specific password to access the imaging program, this has not proven to be a problem. This lack of hand written data also increases the accuracy of the data itself by not breaking the electronic chain of combining the fingerprint image data and the personal data during the printing process. Of course, agencies will have to supervise the use of the machine to ensure that other operators do not use the same passwords and log-on name.

In large agencies, live-scan electronic images are slowly replacing ink as the primary means of creating a fingerprint record. While ink requires that each finger is inked prior to each impression, live-scan allows each finger to be scanned as repeatedly as necessary to generate a clear fingerprint impression, but the best detailed image need only be captured once. The term capture of a fingerprint is that the image is digitally acquired for further processing and subsequent printing.

In general, novice, live-scan, computerized systems operators can produce clearer overall impressions when compared to using ink. Clearer images are the result of the fact that a live-scan operator has no reason to accept and capture a smudged image. While live-scan type print impressions generally result in a clearer overall fingerprint impression database, most fingerprint specialists prefer properly made ink impressions for comparison purposes. Ink allows great detail, if properly done. The problem results from the fact that unsupervised and/or undertrained fingerprint technicians in jail booking areas or public fingerprint counters will often produce a higher percentage of smudged fingerprints using the ink method.

The print can be rerolled until a satisfactory image has been made. Once this is achieved, the operator will move on to the next finger until all 10 fingers are rolled on the glass platen, then the plain impressions of each four fingers and thumbs are made along the lower part of the l0-print card. These nonrolled plain impressions will help ensure that the 10 fingers were rolled correctly. This procedure has not changed from the ink process. The fact that it is much easier to reroll fingers with the live-scan systems seems to generate better overall impressions with novice operators as well. Clearer l0-print cards equal a better database and an improved match, or hit rate, on subsequent database searches.

ARE THERE ANY DISADVANTAGES TOO

The system is not without its disadvantages. The main disadvantages of the live-scan systems are that most are not portable and require high maintenance. The systems and printers must be calibrated often to produce quality fingerprint impressions. Computer-generated artifacts can also be added to a fingerprint impression by the operator, the system software, or by the computer printer. User errors can result in the fingerprint of one individual being added to the information and name of another. These instances are rare they are not unique to live-scan hardware as they can also be found with the traditional ink method.

One of the main reasons for errors with computer-based systems may be because the operator may not always know what data the computer is currently processing. A I0-print card could be fed into a printer which is printing a different individual’s fingerprints. Most systems attempt to avoid this problem by eliminating as much handwritten data as possible by keeping the alpha-numeric data and the fingerprint images together throughout the printing process. A similar problem was noted with standard inked l0-print cards. If the descriptor data, such as name and date of birth, was not added to the fingerprint cards immediately after the printing of a person, it was possible that the wrong information could be added. With current systems, the main problems reside with the reprinting of data from electronic storage buffers, or the printing of miscellaneous l0-print cards that are provided by the customers.

The most notorious drawback of computer-generated fingerprints is not from the occasional error but an inability to reproduce very fine fingerprint detail. Computer-generated images often lack the nuances of a rolled ink fingerprint. These fine details or nuances are often used to compare fingerprints. So the trade-off seems to be that while computer-generated fingerprint images save time and can enhance the computer database’s hit ratio, they can also prove difficult for use in some of the more challenging fingerprint comparisons. The comparison of crime scene latent fingerprint impressions often rely on the fine fingerprint ridge detail.

Generally, exemplar and latent fingerprint impression quality is highly variable. As was mentioned earlier, it is not that uncommon to see crime scene latent fingerprints that are of a higher quality than the exemplar prints on file. Whether the exemplar fingerprint impressions are ink or computer-generated, the actual quality and detail of the print will determine its usefulness in comparisons.

This article has (2239) words

Dr. Anil Aggrawal, M.D.

Professor of Forensic Medicine

Maulana Azad Medical College

New Delhi‑110002