Full-featured photo image editor using canvas. It is really easy, and it comes with great filters. Fairly basic but it's not trying to be the Gimp, it's trying to make it easier to edit pictures. Crop, flip, sketch, add shapes, add text... basic stuff but that's usually what you need. Includes some common filters. Throw it into an HTML page and you're good to go.

Incorporates Google Analytics, but there are directions in the README for disabling it.

Build it yourself, pull it from a CDN, or (probably) download it from the CDN and host it locally.