We recommend png format. If the image is being created in Photoshop, you should also use the "Save for web and devices" option instead of just hitting "Save as" and choosing png. This will do the best compression with the best quality that most browsers prefer. A great benefit of png is that it saves transparency, which is nice for logos and images that are against a dark background.
Article ID: 40, Created: 12/20/2012 at 11:45 PM, Modified: 12/28/2012 at 10:14 PM