What frustrates me most about being an artist (more in hobby than profession) is when the standalone complex of creation happens. More specifically, I can make something on my own, then later on down the line see someone do something surprisingly similar or have someone point it out to me if they happen to be looking over my stuff. Typically, claims of originality tend to be against people who aren't pro or published by this point, even if the thing I'd created was done years before the media work.
Overall, my frustration isn't with the other artist(s) at that point (We just both had the same good idea

), but the people who do throw the hissyfits about rip-offs and plagiarism. Seeing how I'm a fan of medieval fantasy, I figure the genre's been stereotyped to death. You'll either get designs hardcore faithful to an actual medieval era, or you'll get things that might defy physics or common sense just because they look cool. I tend to bounce between the two, myself.
Anyway, I figure if I muster the courage to post whatever to the net, it's basically no longer mine to control. If someone wants to steal it, crop it, make a fancy avatar out of it, or whatever, cool. I'm kinda flattered if they use it in a positive light, honestly. Not so much so if it becomes a posterchild for artistic fail, but I tend to accept my mistakes as someone with very little formal training and feeling like they are slowly improving over time. I do wish I was a lot better at CG stuff, though. Me drawing with a mouse just doesn't mix, and while I'll google a photoshop "how to" from time to time, half the problem is knowing what to search for in terminology.