Photographs and images are powerful tools to use in blogs and wikis (not to mention classroom presentations). Often, however, you want to edit the image--to make it prettier, smaller, larger, different.
In the last several years, free photo editing software is available both online and for download. (You can also use non-free image editing software, which is usually more powerful, such as Photoshop and Illustrator.) Here are some of the more popular free programs: