Whats the best method for displaying PNGs wherever possible, with another format as a fallback?
Server-side content negotiation is the most reliable approach and the only one known to work regardless (almost) of the user’s choice of browser and browser settings. Apache supports it, albeit not very conveniently; Greg doesn’t know about other servers (info welcomed!). The major drawbacks are that you need to duplicate any image that you want to negiotiate (e.g., make a PNG version and a JPEG version); you need access to the server configuration; and there’s no standard approach to setting up content negotiation in servers, so every product is likely to be different. There is no known client-side approach that will work reliably in all or even in most cases. The HTML 4.0 OBJECT tag was the most promising, but it failed due to non-spec-compliant implementations (see the previous question). People have promoted various ActiveX/JavaScript-based methods, but many users (reportedly around 11%, Greg included) disable JavaScript and ActiveX controls for security and/or stability reasons. S
