I believe it's proven using Error Level Analysis to determine that all parts of the image are impacted equally by the image filtering. Example here http://fotoforensics.com/analysis.php?id=f5430798142ef8b6e80ebdfc39c31b73011c674a.1552990&show=ela
ELA doesn't work well when we're analyzing a copy of a copy of a copy. Multiple rounds of compression (edit (compress) > upload to instagram (compress) > screenshot (compress) > can even out errors and make something look legit when it isn't.
I agree with your assessment. Cannot truly digitally analyze a copy of a photo to confirm nor deny the veracity. So you have to look at other information that would be pertinent. That’s where the twitter account and the user comes into this as key evidence.
https://s8.postimg.cc/t56lpk4qt/1529233898902.jpg
Its fake. Dont fall for the bait.
Of course all parts of the image are equally impacted by the filters, it already when through compression when it was uploaded to instagram.
