Hi, Kat. In CS versions of PS simply click on the 'T' text tool in the tool bar to set up a text layer and add a copyright symbol by holding down the Alt key and typing in 0169. You can add your name and date if you want to, or you can enlarge the symbol to cover the whole of the centre of the image, and then, as Alan has suggested, fade the opacity until it is almost invisible to the eye, but would render it useless for anything other than the purpose for which you intended. Don't forget to merge layers when you have done it.