Instructions
Post a copyright notice on the main page of your website, and in each individual picture. Depending on the type of program you use to edit your pictures, you can change the domain of the picture from "Public" to "Copyrighted." This is usually done in the "Image properties" or "File info" screen. Include in your copyright notification that individuals or companies caught using or copying your pictures will be prosecuted.
Change the resolution of the picture to 72 dpi from its current resolution. A good minimum resolution for printing is 200 dpi, and that is primarily used for newsprint. Photos that are printed for personal use or display are generally printed at 300 dpi depending on the size. Images that are displayed electronically can be shown at a 72 dpi; this will allow the picture to be viewed on the screen, but if printed the picture will be very small.
Add a watermark to you picture. If your website is hosted by a company that caters to professional photographers, they will likely have an option where you can easily add a copyright watermark right across your picture. You can also add a watermark to your pictures directly using your photo editing software.