If you're worried about people pinching photos from Flickr, either cover them with watermarks (which doesn't do them many favours and can still be removed with some time and effort) or don't post any high resolution large files. Personally, I only use it as a host for shots I post here, not so much to stop them being nicked as that I far prefer to show off my shots as decent sized prints. The shots I do upload get resized to 800 pixels on the longest side and reduced to >200kB file size, enough for about a 3"x2" print at the oft quoted 300DPI resolution although a 6"x4" print isn't too bad.