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Date: Tue, 2 Sep 2008 17:33:59 +0200 (CEST)
From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: FreeBSD <freebsd@optiksecurite.com>
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Cc: freebsd-questions@freebsd.org
Subject: Re: How to compare 2 images from command line
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> I'm trying to determine if 2 jpeg images are identical. The images are 
> screenshots taken with scrot at different times. The point is to know if the 
> display is working correctly. I tried to use 'diff' but without success, 
> probably because of the metadata included in the image. I also tried the

cmp does byte-to byte comparision.

if you want to make sure uncompressed bitmaps are the same then uncompress 
(cmp) and then compare