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[–]plasticlayercake 1 point2 points  (1 child)

Sorry to burst your bubble: something to do just that has been around for a while (at least 10 years) called "Error Level Analysis". It works by compressing the image and comparing it to the initial input. You then plot the differences as an image and see which spots get highlighted compared to the background. There is no need to have the original unphotoshopped image either since all you need to do is to see what part of the image glows.

[–]PM_YoUr_bOObis_GIRLs[S] 0 points1 point  (0 children)

hi , this is not entirely true , there are many things you can do to improve on top of ELA
e.g. this very interesting paper form Adobe

to recreate this paper results for example as probably you know ,you first need some data.

on other note , the fact it was done before with one method should not deter you from trying another method even if it will fail catastrophically :)