Easy Watermark Plugin for WordPress

Easy Watermark is a WordPress plugin by szaleq that allows you to add image watermark to every single image or all images from library at once. It can also be configured to automatically watermark new images as they are uploaded. Watermark can be a png, gif (alpha channel supported in both cases) or jpg image. It’s also possibile to set watermark opacity (doesn’t apply to png with alpha channel).

Download: http://wordpress.org/extend/plugins/easy-watermark/