[Image-SIG] Determine byte offset of JPEG SOI marker

[Franz Buchinger]

Hi,

I want to implement some sort of "post header checksum" for JPEG images,
i.e. the checksum should only change if the actual image data was altered,
EXIF/IPTC metadata modifications should have no effect. My plan to do this
is to scan for the JPEG SOI marker, read n bytes after this marker and
calcultate an MD5/SHA checksum for this.

Can PIL tell me the byte offset of this marker?

Greetings,

Franz
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