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Date Posted: 20:24:59 07/31/04 Sat
Author: Al Christoph
Subject: Signatures of JPEG's

If this subject has been raised before then forgive me.

In using the JPEG can read routine, I discovered that a portion of my sample JPEG's would not pass. The problem is two fold. First can read totally ignores files with an Exif signature. Secondly, it ignores weirdo's.

In a sample of 3500 jpeg's all of whom could be read by Envsision, I found 69 different headers!!!

My strong suggestion for the future is that you test only the first three characters of the file for JPEG compliance. The remainder of the ten character header simply does not appear to be predictable enough at first blush to make it worth testing. So leave it go at $FF $D8 $FF.

Regards,
Al

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