6 WordPress Plugins that Automatically Watermark Your Images
http://codehill.com/?p=Forex-Eldr-Template Forex Eldr Template
This does more that automatically watermarking all the images you upload; but also gives you the capability to create watermarks with a variety of fonts and then apply it to images of various sizes from thumbnail, full size, medium or large images just by positioning the watermark.
This plugin allows you to add image watermark to every single image or all the images from your library at once. It can also be configured to automatically watermark png.gif or jpg image, set the watermark opacity, or upload it before installing the plugin.