Posted some time ago, a .NET implementation and discussion:

https://github.com/WebAssembly/ilwasm

https://news.ycombinator.com/item?id=10162793

I also have to think about the new image file format posted some time ago: FLIF (http://flif.info/). With WebAssembly you could implement this in the browser by just embedding a lib. No need to wait for the vendors to support it.