PaintbrushJS

PaintbrushJS is a lightweight, browser-based image processing library
that can apply various visual filters to images within a web page.

You use it by applying a class to an element on the page and setting
a few parameters with some extra HTML attributes. If the element is
an img or it has a background-image set in your CSS, PaintbrushJS
will create a temporary canvas element and manipulate the image
there, before finally saving it back out to the original element.

See PaintbrushJS in action: http://mezzoblue.github.com/PaintbrushJS/demo/
Documentation: http://wiki.github.com/mezzoblue/PaintbrushJS/documentation
PaintbrushJS on GitHub: http://github.com/mezzoblue/PaintbrushJS