Here's something I've always been curious about, but never thought to ask. Is it valid to reference say an image created dynamically by php that responds with the correct meme type, but still has the .php extension? For example, <img src="/lib/background.php?color=333333" alt="" /> Is there anything that is negative about this approach? I don't always have mod rewrite available to hide the fact the image is dynamic.
The browser does not care about the filename. All it needs is the correct Content-Type header in the response.
Check the first example here: http://php.net/manual/en/function.imagejpeg.php