On this page you can test what image formats your browser supports.
Normal web browsers only have to support JPEG, GIF and PNG.
PNG indexed color
The BPG format by Fabrice Bellard may very well replace the JPEG format in the future, as it offers all the benefits that JPEG2000 never really managed to pull off to a sufficient degree, such as a greatly improved quality vs. file size improvement, transparency support, support for different color spaces and color profiles, EXIF, ICC etc. Browsers will hopefully soon be able to display this image.
Your browser does not really have to support these to be compliant.