I would suggest starting here with the JPEG (JFIF) specification.

You'll have to uncompress and determine what makes up those RGB values.
Not having specific knowledge in this domain I can't help you much more than this - I don't know if a package already exists for this or anything more.

HTH

In reply to Re: Replace certain color in jpeg by RazorbladeBidet
in thread Replace certain color in jpeg by jkva

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