Amber has been investigating which image formats make sense for which situations.
Choosing image format is only one step towards optimising images on the web. There are many, many other steps to consider, and so, so much to learn!
Alas, it turns out that it’s reliant on user-agent string sniffing. I guess that’s to be expected: this isn’t something that can be detected directly. Still, it feels a little fragile: whenever you use any user-agent sniffing tool you are entering an arms race that requires you to keep your code constantly updated.