Along with all the other stuff you can find, the Internet is a great source for images. Whether you are looking for a photo of Billy the Kid, a diagram of a combustion engine, or a picture of a four leaf clover, chances are some one has put it on their Web site.
Rather than searching the general search engines, try limiting your search to an image search engine such as Yahoo! Images or Google Images. Yahoo now claims 1.5 billion images and Google is a close second with 1.1 billion.
Source: LibrarianInBlack