I don't. What do I care if someone wants to use them? I'm not making any money out of my photography, I've had my fun by going out and taking the photo. The only time I might object is if someone else did make money from it.
But for most people who want to use a picture as a desktop background or put it on a blog somewhere, what's the harm?
I ususally just pop my name in the right hand corner where it is relatively unobtrusive. I may start changing this but at the moment I honestly can't figure out how to effectively store small resolution images and large resolution images without constantly getting confused between which one is which. I'm sure I'll figure out a system! Also, I still have no idea what meta data is
I've never put watermarks on my work. It's one of those things that's seen as 'pro' but there's really no need unless your work is worth hundreds/thousands. As a result, it's one of the phases of photography. You know the one where the only things you shoot are horrible, clichéd scenes? Those clichéd scenes will probably be watermarked
I don't watermark or sign photos, unless a friend or acquaintance asks for a copy for their wall, then I add my signature, it is not for my benefit, but makes what is framed on their wall look a bit posher. I started doing this because the first person who asked, asked me to sign it and gave that as the reason. I am not charging for these by the way. I give them a digital copy so they can order the A4, A3 or a canvas.
As I mentioned in another thread when putting images on-line I go for very high compression even at the risk of artifacts and generally upload at 1080 pixels.
I agree with Thesownrose but as was highlighted in our local flickr group some folks take advantage for commercial purposes which does annoy me. A member went to a local pub restaurant to see one of their images framed on the wall, further investigation revealed several other members images used the same way from the group pool.
The image I have had linked from the BBC nature page in recent weeks is a good example, if someone liked the shot and managed to print it for their wall (many printing services will interpolate for you) I don't mind. One of mine, a bumble bee in flight recently ended up on someones blog, with a comment "WTF is this real ?" again I don't mind. Although it would have been good manners to ask. When the BBC actually wanted an image for the main news website, the journalist contacted me to ask permission and for a TIFF as the flickr copy is scrunched as described above and I was happy to oblige.
i do this to my images that i take of bands but not usually on any other images i take. i only do it help get my name around i guess, and i only put it small in the corner, so if a band uses it on fb or something then it's nice to know that my name will become more known i guess.
I have seen the internet postings of someone who takes all these landscape pictures and then watermarks the **** out of the main focal point. Then when you mention that the picture would be lovely if it wasn't for the distracting watermark, he flips out and tells you you're wrong.