I haven't done complete browser testing, but I know you can use a PNG and simply change the extension to .ico and it will still work in some browsers. Edit: I

I haven't done complete browser testing, but I know you can use a PNG and simply change the extension to .ico and it will still work in some browsers. Edit: I tested on a domain that previously didn't have a favicon. Putting a PNG named favicon.ico at the root without an explicit <link> worked in Chrome 9, Firefox 3.6, and Safari 5. It didn't work in IE 9.