Ive seen several people just post a picture with no explanation of if its there's or not so you dont know whether or not to flag it.

Yes, you're absolutely right! This is very annoying in photography posts.

We have a small piece about plagiarism in the Steemit FAQ, but I'm not sure how many people even visit it. I think it should be more prominent. Whenever there's someone suspected of plagiarism, I think they should be informed, so they can avoid this in the future. Heck, a bot like @cheetah could even write up a little post about plagiarism and correct sourcing (aswell as double-sided proof of ownership) and link to it in their comments. That way the comment stays small, but the information is there for the taking.