Picmarker is a watermarking tool which is quick and easy to use for copyrighting images or even naming students digital work.
Some of the features are:
• upload files from your computer or grab them from your Flicr, FB or Picasa
• add text watermark, image watermark or tiled watermark
• no need to download or install software
• free - unless you want the pro version with a few more bells and whistles
I used picmarker to watermark my class avatars. Our class uses a number of wikis as part of our online learning management system and students use avatars to identify themselves on these wikis. Although the students recognise themselves by their avatars, their teacher needed some other way of identifying them easily for management of work purposes.
Here is an example of what the watermarked avatars look like. Click on the image to enlarge.