Many images can be found on the internet that are published under the so called “Creative Commons” license. This means that as long as you credit the original image as specified by the image author, you can alter and use it without paying any royalties.

Wikipedia maintains a full collection of images published under this license, which is a great go-to place to find pictures of just about anything.  And most of the pictures on any topic in wikipedia itself are covered under this license. So I’d recommend two methods for searching for these images:

Method 1:  Search a topic on wikipedia, see if any of the articles include pictures, click on the picture you’re interested in. You’ll get to a page with info about where the picture comes from, plus usage information. Scroll down for the “Licensing” section which will tell you exactly what license it’s published under (look for anything that includes “Creative Commons” in the license title), and any specific instructions the author requests for republishing (most often it’s how they’d like the credit worded).

Method 2:  Go direct to the source,  The Wikipedia Commons, self described as “A database of 4,985,404 freely usable media files to which anyone can contribute.”:

http://commons.wikimedia.org/wiki/Main_Page

A searchable and topic-indexed collection of pictures, audio, video, etc. that are all published under one or another form of the Creative Commons. Once you find a pic you want to use, do as recommended in Method 1:  look at the licensing info, and away you go!

Of course there are lots more places on the internet to search for uncopyrighted images, but this is an easy way to get directly to a large collection of images that you know are published under Creative Commons.

More information about the Creative Commons license and its forms can be found at the website of the nonprofit Creative Commons corporation.