If you upload images to the net, you may well lose the rights to them. To safeguard them, the easiest thing to do is watermark them with a tool like iWatermark.
If your photos aren't particularly important, then protecting them with a watermark won't be of much concern but if you're a professional photographer, or if you use images for commercial use, then it's a real issue. Adding a watermark is a simple way to protect your images from illegal or unauthorized use. iWatermark is a very powerful and effective way to do it too - it provides just about every conceivable control over how you wish to add your watermarks.
To get started, simply drag and drop an image into the 'Input' panel. Then click on the output panel to select where you'd like to save the new file. It would have been nicer if a preview of your image appeared in the input panel but instead it's replaced by a generic icon. However, after this you have maximum control over how your image is handled and processed including the editing of EXIF and metadata. Note that iWatermark leaves the original files untouched but creates new images complete with the watermark of your choice.
In this trial version, you're limited to eight different example watermarks but the important thing is processing takes a matter of seconds. You can rotate, resize and reposition watermarks to your heart's content making it a truly customizable and powerful watermarking application.
Overall there's little to fault with iWatermark. From Meta-data preservation to embedding IPTC information, iWatermark covers every possible watermarking need for the amateur photographer.