PixPlugin (http://www.pixplugin.com) is a simple service that provides free custom images inside your website or blog. You simply write HTML image tags for the images as if they exist, and they magically appear!
This Auto-Inserter plugin for wordpress automatically creates a PixPlugin image tag in each of your posts. The terms for generating the image are extracted from the text of the post, to try and find a relevant image. This is a great way to give some color to an otherwise dull blog.
Note that if you prefer more control of the images you can just use the PixPlugin service alone, without this auto-insert plugin.