iWatermark is a graphics editing tool that allows you to watermark images. This application was designed to let you process multiple images at once. The graphical user interface is proof of that. It allows you to simply drag and drop images or tell the application where the images you want to watermark are and where you want to put the watermarked images. iWatermark comes with 7 different watermarks that you can use to test the application, and, of course, you can use your own ones. You can create new watermarks from the Watermark Editor. You can use image or text watermarks. There are quite a few settings for you to play with, including effects, transparency, backgrounds, etc. The location of the watermark in your images can also be customized.
Other than watermarking, this application will also let you convert your images to various other formats. You can enable this feature in addition to watermarking or you can simply use the app as a file converter.
All in all, this app seems to work very well and it has lots of customization options. Make sure you visit the website for a complete list of features.