I will state this here, as I did so in a comment elsewhere.
For those who do not know, Wallpart is a website form a Russian company which makes prints of images from the web, usually from basic image searches on various search engines. People seem to think they are committing "art theft", but this is not the case.
1) This is a Russian company. Therefore, they technically do not have to follow any laws except Russian laws. I am not a lawyer, but I am fairly sure that Russian copyright laws do not mesh well with US/EU copyright laws.
2) They are not storing any artwork on their own servers, which is the primary reason they are able to have such a service. All of the artwork you see is from Google Image Search, among other engines. They even state that they simply link their site to search engines. It is similar to someone going to Kinkos or a similar physical store and asking for a print from a USB drive.
3) Due to a combination of 1 and 2, what they are doing is technically not illegal, though it can be argued as immoral. Unlike actual art theft (claiming ownership of the copyright or attribution for the artwork, or uploading artwork that does not belong to them), this is simply a service similar to what is given by many professional and independent printing houses in the US and EU, only using the internet as a method to find images to print. They do not claim ownership, nor do they actually post any of the artwork themselves, which means that there is no actual art theft occurring.
I many not agree with what they are doing, but if you are honestly offended by what Wallpart is doing, the only option is to make it so that your artwork does not appear on any search engines, and that is assuming that their users are only using that feature. You cannot legally stop someone from obtaining a print of a file for personal use, at least not in the US.
Unless Wallpart begins hosting files themselves, what they are doing is completely legal, whether an artist likes it or not. End of discussion.