Automatic Thumbnailing and watermarks
You can have your own watermark to overlay your images, if you like. Use an image with a white or black background, and the background will disappear. The remainder of the image will be made translucent.
The watermark image name, the location of the watermark all can be set in the site preferences.The color to be transparent is a little trickier, and needs to be set up by the webguy.