Here are links to a couple of sites that point out some of the legal issues with posting photos on a stock site like RGBStock. People who take photos in public places need to ensure that they have the legal right to post those images for stock. Remember, the buildings quoted in these articles are just a handful of examples, and you need to check before uploading. There are lots of good articles online about this subject, and if you take photos in public places or on commercial premises, you should understand the law of the country in which you are taking the photos.
Copyright is a very complicated issue because its selectively enforced around the world. Photography copyright isn't really enforced in Asia except in extreme cases with lots of money involved.