Checksum JPEG data (not the whole file)?

One easy way to get a hash sum of just the pixel data would be to convert the JPEG into a 32Bit BMP or alternatively into PNG and to calculate a hashsum from that. This will strip all the associated information from the JPEGs and would even match JPEGs with differnt encodings that lead to the same pixel data. You could of course also use the in memory pixel data of the resulting BMPs directly if you have it (i.e.

Windows has several API functions to get it from any supported image type).

Yes to jpeg and exif, I don't know to the others.

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