The act of claiming that you created a work of art so that you can get in on a small share of the praise and attention that is lavished on the best artists, without actually having to have any artistic skill whatsoever.
Since artists are incredibly vain, terribly insecure and need praise to survive in the same way animals need oxygen, Art Theft is considered the eighth deadly sin on online art websites such as DeviantArt, SheezyArt and StormArtists. Being an art thief gets you banned and sent straight to hell to burn for all eternity in the flames of the site's members.
Warnings pointing to this fact can be easily found in the thousands upon thousands of poorly made "Anti Art-Theft" stamps and clubs available on said websites. An ironic fact is that 95% of the people who bitch about art theft do not actually have the artistic talent to make their art worth stealing.
Being vocally against art theft on these websites increases the size of your e-penis by up to 200%.
Art Theft is generally practised by emo 13 year old boys who are so desperate for praise and attention that they will gladly accept it over the internet for something they didn't even make. If this is you, you should kill yourself.
"OMG Some horrid person posted a Sonic recolour that was the same as mine!!!11 I am so reporting them for Art Theft!"
"I'm so hardcore against art theft, I'm going to make deviantART's twenty thousandth anti-Art Theft club!"