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Identical photos?

I need a program that will tell me if two jpg photos are identical, and if not, how many pixels are different, and where those pixels are located.  I assume that a program that could do this could work with various resolutions of jpg.
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hcsorensen
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hcsorensen
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lherrouCommented:
hcsorensen,

If you're saying, you want a program which can eyeball two pictures of different resolution, and tell if they are the same photo (as can easily be done by the human observer), you aren't going to find that (maybe contact the DoD or CIA, they are known to work on these kinds of issues). If you need a program to evaluate two photos and review amount of total differences you should take a look at the ImageMagick "compare" command (http://www.imagemagick.org/script/compare.php). This command returns qualitative results and can also return a "map of changed pixels", so if you are comparing amount of change in different forms of image alterations (compression, sharpening, etc), it can give you a numeric value and also a picture of the density of the changes in the image.

Cheers,
LHerrou
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hcsorensenAuthor Commented:
Many thanks.  Right on target.  I think this solves my problem.
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lherrouCommented:
Great. I hope it does the job. And thanks for the points and the "A".

BTW, here's a site using the compare command to show differences between compression in JPG and PNG file formats, it illustrates what can be done: http://www.fractalus.com/info/png-jpeg.htm
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