So below are the solutions to different cases

Please tell me which parts are wrong or fine.

Below links' images are NSFW.

Same type, Same resolution, Different size

case 1

if the image has not been uploaded, choose the biggest size

else, check their differenced image,

> if you can see the slightly colored outlines in it, then you can reupload it.

> if you cannot see the slightly colored outlines, then don't reupload it.

Different type, Same resolution, Different size

case 2

(?)Same as above

Same type, Different resolution, Different size

case 3

(?)compare two images by eyes ( zoom in )

Different type, Different resolution, Different size

case 4

case 5

for case 4 and case 5, both of them need to compare two images by eyes ( zoom in )

but in case 4, I thought B mostly wins.

Edited:above images are all from artist's websites, and two images' SSIM > 0.9 but not equal to 1