Aphex_Twin

I want to do the following thing for a website:

1. Present a user with tools with which to construct simple bitmap graphics (primitives for points, lines, circles, etc...) - in the form of buttons and mouse actions. All laid out in a page.
2. The possibility to save that into a gif or pgn.


I think Javascript would sound suitable for the first thing, but I don't quite know how to create an actual bitmap or how to save it on the server.


Right now I have some basic HTML skills, can work with PHP/MySQL and can generally figure out Java Script.


What I'm looking for is a kind of pointer, nudge in the right direction or some advice on how to do the above.


Edit: As a secondary question... Is there a way to detect if a text string (like: "http://something/somethingelse/something.extension") points to a picture (a gif/jpg/png) or to something else?