Oh, this is actually neat:

> what about progress bars for stuff that your server is doing in the background

This seems like a really good micro-service.

Yes, the idea is brilliant! But the purpose of my source code is to use "real-time" gif images in mail clients. Unfortunately, videlalvaro's solution is only possible for mail clients which support loading images from its original source. Google loads the images from their proxy, which downloads the images first. It DOES re-download each image at the moment you re-open the e-mail message, but it won't make it possible to manipulate the images real-time. I've tested it. It does work in clients like outlook, cause outlook shows the images from its original source, but gmail doesn't. So sending a gif image with a certain amount of frames is better, in my opinion.

Yep, i was expecting OP's code to be the PHP implementation of that, but a quick look at index.php shows its not. Streaming gif frames, now thats what i call a live gif.