[Question] Signature calculation ignoring parts of binary files

I feel really bad asking this, and I should know the answer, and yet.

I have a binary file that needs to go into a repo intact (unchanged). I also have a program that interprets the contents, like a textconv, that can output the relevant portions of the file in whatever format I like - used for diff typically, dumps in 1K chunks by file section. What I'm looking for is to have the SHA1 signature calculated with just the relevant portions of the file so that two actually different files will be considered the same by git during a commit or status. In real terms, I'm trying to ignore the Creator metadata of a JPG because it is mutable and irrelevant to my repo contents.

I'm sorry to ask, but I thought this was in .gitattributes but I can't confirm the SHA1 behaviour.

Sheepishly, Randall

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 NonStop developer since approximately 211288444200000000
 UNIX developer since approximately 421664400
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