for younger people, this is already solved by noticing each online system corruption of the image. e.g. some social networks add a greenish tint, other have a bug that adds an also greenish (but stronger) tiny to only the last column of pixels, etc. then by looking at those artifacts you can know not only if it's a repost but for how long it's been reposted.

it's a skill we, older, not so immersed, totally miss.