I have found it more frequent that I see stolen and re-posted artwork on popular art sharing websites such as Deviantart.com as an example.
As an artist myself, I find it a disgrace that 3rd party reports of art plagiarism are not taken with more action, as it is still not right to sell and / or claim another person's work as your own and / or gain profit. I find it stupid that only people that are the owners of displayed art online can make a 'valid claim', yet if they don't the website keeps the stolen art. Here is what I don't get:
IT IS STILL ILLEGAL TO MAKE PROFIT OR RE-POST WITHOUT VALID PERMISSION, ESPECIALLY IN CASES THAT THE PEOPLE COMMITTING THIEVING SELL THE STOLEN ART.
Tighten image / art copyright laws on websites such as deviantart.com to make a more cleaner internet.