"so long as the person using it didn't MAKE A CLAIM they created it themselves.

But is that claim implied on Steemit?"

It's implied on INTERNET: "if I don't sign it, it is not mine; I obviously took it from another source".

Which brings a possible good idea:
There's plenty of "blank" space at the sides of the post, It would not hurt to have a "box" where the sources are displayed at (at least for the images directly linked outside of steemit's URL system).

If they "stole" them (so to speak). It's neither steemit's or the author's problem, but of the page where the image is hosted at.

In the case of text, anything written/typed is implied to have the author rights of the username. Otherwise it is blatant plagiarism. Because, yes, any decent writer uses quotes whenever the text is not theirs (again, use google to find the original source if it's not stated).

We've access to the whole communal collection of human information at the tip of our fingertips. We HAVE to use it.