Though this site talks a great deal about textual plagiarism, images plagiarism is actually the most common kind of theft on the Web. This is due somewhat to misconceptions people have about copyright law and the ease with with which the content can be lifted but is mainly owed to the fact that most people lack the photography/drawing/painting/image editing skills in order to produce good, high-quality images for their site. Essentially, they can write their content, just not make the images to go with it.
As a result, people have to “steal” images for use on their site. Though sometimes it’s legal, for example taking photos from the Stock.xchng or from sites with Creative Commons Licenses, it often times is very unwelcome and, since images are almost never credited, becomes a form of plagiarism.
However, the image overlay trick is just one of many that can help protect your images. We will be discussing many of the others ones in the near future. I just wanted to offer something right now for those who have been asking me about image plagiarism.