I tried this Simple Image Watermark.
Realizing it hasn't been updated since 2012. It uses the old Media Library layout which was used back then. So there is some layout issues.
Also since the WordPress admin was redesigned the admin menu is missing some padding. http://cl.ly/image/1K1B0T1T1I2F
Both issues are easily fixable with an update to the plugin to the newer standards.
I would like to see a watermark image size to be available as I wouldn't have to resize and re-upload.
On the minor front the plugin also has some spelling mistakes in the admin setup.