|We're talking about the date imprinted when the picture was taken which is not necessarily the file date, right?|
Open the jpg in notepad or wordpad or something that'll accomodate its size. A jpg file isn't a text file so most of what you see will be gibberish. However, as far as I know the date is text. I tried it with a 50 K camera phone pic and the date showed on two consecutive lines, along with the time. It was near the beginning of the file and was fairly obvious.
Assuming that's all there is to it, you just need to edit in a different date. You might want to experiment first with copies just to make sure that works OK.
No doubt there's other photo editing software that can change the date imprint but if treating it as a text file works then you don't need any of that.
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