Automatically watermark images as they are uploaded to the WordPress Media Library.
The Plugin example doesn't work in this latest install.
Once the plugin has been applied all of the images uploaded are watermarked in the center with a logo and can't be undone even after the removal of the plugin. So the plugin does work, but watch out what's done can't be undone…
The plugin give you options of which you can't turn on unless you purchase the upgrade which you are told about in every single screen and every single instance of plugin.
I have never been a fan of the hard sell. But that is just a personal opinion.