If you're a small, independent publisher -- so small that you even do your own book covers -- you are problably often left scratching your head and wondering where you can find a suitable image which won't cost you $250 (or whatever currency you work in).
Well, here's a possible solution. It's called Stock.exchng. The stock part is a reference to 'stock' photography, which normally means a huge commercial library of prints, from which you make a choice and then pay the aforementioned $250 or whatever. But in this case it seems to be... well, free.
I haven't explored the small print in any detail, but you could start with the FAQ, in which it says that you can use the images for web sites, magazines, books, CD covers, and so forth. Free of charge.