Picnik is photo editing online, in your browser. It gives real people photo editing superpowers. It's fast, easy, and offers tons of powerful tools, artistic effects, stickers, frames, touch-ups, scrapbooking tools and more. And that's all for free.
This add-on integrate this service into Plone.
Some useful links about picnik:
How to install
You can install it as any Plone addon, following this documentation: http://plone.org/documentation/kb/installing-add-ons-quick-how-to
How it works
Picnik support different way to get and edit your image and to get it back. In most of the case you can not work with this add-on in localhost. You must try it with a server accessible from outside.
This add-on provide two browser page: @@picnik_edit to redirect to picnik editor and @@picnik_handle_pull to get image back to Plone.