mc-3dskin allows you to easily request Minecraft skins in various formats for your PHP-powered website. I personally use it for my website http://hypixel.maxkorlaar.com. It's got built-in support for caching the images on your website which, trust me, speeds up things a lot. I recommend you to periodically clear your cache folders (I forgot to do it for a few months with the aforementioned website, and it stored over a few hundred thousand files).
I've also included my own MojangAPI PHP class which allows you to request a Mojang profile based on an UUID. You can use such a profile to request the current username of that profile.
I have uploaded this so people can take a look at my code and help improve it 😄. Read LICENSE carefully. (In short: Provide attribution when using this project, and please notify me so I can check out your work) And, please file bugs and/or pull requests. Improving this helps us, and you!
Uses https://github.com/Sybio/GifCreator, and 3d.class.php contains some more info about its authors.