CLPEX Chat Board

We have a small dilemma that could use a few insightful opinions:

Processed evidence using Ninhydrin. Latents developed were captured digitally. Approximately a year later, it was found that the digital images were captured below the 1000 ppi guideline that SWGFAST suggests for using digital images for comparison. It was decided that the evidence would be checked back out and re-shot at the 1000ppi + guideline (soon to be standard). Unfortunately, the ninhydrin prints had faded over time and were not as clear and "bold". A few impressions could not be ID'd using the re-shot images because the ridge detail is just not clear enough, but if the original images were used (I believe the resolution was between 400-500ppi) the ridge detail was clear enough to affect an identification.

Anyone have procedures in relation to this type of problem?

Thanks for your input.
Kim

Kim,

Is there anything in YOUR SOP's stating a minimum resolution standard? If not, then there's nothing wrong with doing a comparison with images that are below the SWGFAST guideline (that could become a standard) of 1000ppi, as long as the quality/quantity are sufficient for individualization. As long as the image meets the requirement of properly representing the item photographed, and it meets the threshold of quality/quantity sufficiency for your examiners, there's no reason you should be limited by a resolution 'standard' that has no scientific basis for comparison resolution (think 'point standard').

But if you have SOP's in place stating that you have a minimum resolution of 1000ppi, and no caveat for lower resolution images, then you may have a problem down the road.

This is one of the reasons why you should comment when drafts for comments (especially for something stating to be a standard) is produced by a SWG that you don't agree with. My personal opinion is that a 1000ppi requirement is one of them.

I agree with Steve. You have no problem using the older images. We really need to stop focusing so much on the technology and get back to the science of the fingerprint comparison. The technology is simply a tool. An image captured in 1995 with a low resolution digital camera and matched to a suspect is no less a match than one captured in 2008 and matched to the same suspect. If we take digital out of the picture an go back to film does that mean that a 4x5 photo of a latent print is acceptable but a 35mm is not? SWGIT and SWGFAST specs should be a "GUIDELINE" not a standard. When writing your procedures never box yourself in. Technology is always changing and you do not want to get in a position where 5 years worth of work is invalidated by a poorly written procedure when there is really nothing wrong with the work.

I have been teaching image enhancement and working with latent imaging since the early 1990's. I think the SWGFAST 1000ppi standard is misguided. I also think the documentation of digital imaging processing techniques they require is unneccessary and will cause more problems than it solves. It does not take into account changes in equipment and technology. You may enhance your images on your nicely calibrated lab system and then be asked to use your documented technques to reproduce the process in court. If the image looks the same in court, displayed on a projection screen, as it did on your nice 22" claibrated flat screen monitor in your lab, you should play the lotto. Also, some enhancement is trial and error. Some things work on some images some don't. Do you record undo's? How does a page of undo's look to the jury. This will especially be true for people learning to use Photoshop or other enhancement tools. This simply gives the defense the ability to draw attention away from the comparison and puts the attention on the technology where it does not belong!

This has all been really helpful and I'm sure our unit will have a lengthy discussion in regards to all of this info.

Thanks!
Kim

Image quality can be lessened to different degrees by all of the following causes (and many more):

1) Improper lighting for the specific situation
2) Improper exposure
3) Motion blur
4) Out of focus
5) Incorrect filter for photoluminescence
6) Low resolution

To tell the truth in my career I think I have seen more problems with 1-5, than #6. If the person taking the photos is well trained and practiced, satisfying the above requirements becomes intuitive. If not, resolution can be the least of one's problems. In all cases we should be reasonable, and my suggestion is that if the lower resolution images are better than the high resolution images, then those should be used.

I'll add just one item that hasn't yet been raised. I think many people believe that the 1000 PPI is a requirement, rather than a guideline; and I believe that many people either scan their images at exactly 1,000 PPI or resample their photos to 1,000 PPI. I'd suggest that this isn't the proper approach for optimal image quality. For instance - suppose I own a scanner that has a 1600 PPI native resolution. If I scan at 1,000 PPI, it is probably scanning at 1,600 or 800 PPI and then resampling to 1,000 PPI, causing some image degradation. It's possible that an 800 PPI scan would provide a better result - because that would be a native resolution of the scanner and there would not be image degradation through the resampling.

And, to the your specific question - as the others have stated - if you have images that have enough resolution to see the level of detail necessary to individualize the print, then you have enough resolution to individualize the print, period. And don't forget - probably 3/4 of the agencies in the US have never even heard of SWGFAST, and they are working with fingerprints every day without any problems.

George