I don't think computer-generated works will be easily distinguishable from human unless they're desired to be or shipped with metadata. It's already hard enough to distinguish human artists from other human artists without having names attached up front.
Yes, and tracing counts as art fraud.
Collage is a bit different, because you are mixing many clones of many other objects such that you create a new object; additionally the way you assemble the clones may transform them (a photo of the mona lisa has different surface texture than a painted version, even more different if it is clipped from newsprint), but while the borders of this are not clear, it is clear when people are far enough over the border. Think of hip-hop, sampling, and remixing music, and some of the legal battles which have come out of that.
I just spit out my coffee, turns out I'm not a bad artist, I'm actually a fraudster!