I can't understand why so many photographers put large images on the internet without watermarking them. They must be bloody stupid. Images like these are crying out to be copied. So I think some of the blame rests on the lazy copyright holders.
As anyone who has ever tried to remove a watermark in Photoshop will know (er, ... so I've been told!), watermarking is the way to go to keep your images from being copied. The onus is on YOU!