Select Edges allows you to accurately detect a photos edges.
BS Editor: The Select Edges plugin is a powerful tool for selective processing. You can select edge detail in your image for sharpening with Unsharp Mask without getting halos or switch to the inverse selection and use Gaussian Blur to diminish the background.
Download the Macintosh (440 KB stuffit file) or Windows (380 KB zip file) version of the plug-in, along with a PDF file that explains its principles of operation, installation and use. The plug-in can be used with Adobe Photoshop 5.5, 6, 7, or CS for both 8 bit per channel and 16 bit per channel Grayscale, RGB, LAB, and CMYK images.
A free component of Optipix you can free download Select Edges 1.0 now.