The javavp8decoder project has now progressed far enough to successfully decode keyframes, and as a result, WebP image files.
A Java ImageIO plugin has been created for testing. It should simply be a matter of adding it to the classpath to take advantage of WebP files in existing ImageIO based Java applications and applets. This is a pure Java decoder, no native code or security exceptions are required for it to function.
A simple gallery applet has be setup at http://javavp8decoder.sourceforge.net/ to demonstrate the decoder in action.
There are some know problems with the current implementation:
1) It's not optimised for speed at all and is quite slow.
2) The loop filter produces slightly incorrect output on macroblock edges.
3) Handling of frames with segmentation is incorrect (per segment adjustments aren't applied).
4) Logging is enabled.
The license is GPLv3 for now.
Gallery Demo: http://javavp8decoder.sourceforge.net/
ImageIO plugin: https://sourceforge.net/projects/javavp8decoder/files/
Project page: http://sourceforge.net/projects/javavp8decoder/