Here’s another site to add to my list of excellent online paint packages. Psykopaint has been created “as a new tool to enable users to express their creativity with a mimimum of knowledge and skills”. It lets you paint over the top of an existing image using a variety of different tools. A slider will let you reveal the image underneath. Or you can just start with a blank canvas.
It’s great fun and well worth taking a look. http://www.psykopaint.com