Nope, you won't get banned on bitcointalk for image plagiarism even if its proven that you took image from someone else and presented it as your own.

For example of something like that, take a look at this case from few years ago when I exposed someone who took someone else's image and explicitly presented it as his own in order to fish some merit. Even though it was proved that it wasn't his image (I contacetd the original creator who confirmed me that) and he even admitted plagiarism, mods did nothing and all he got were few tags.