Keep tabs. See what people are pinning from your blog by going to: http://pinterest.com/source/YourBlogURL

 and

Do a reverse image search of your jpeg art images.

You can do a reverse image search using TinEye http://www.tineye.com

This little kid explains how to do a reverse image search–

If you have found your art used by others without your permission, here are some organizations that can help–