Is the red dot actually where the mouse is? I.e. does the red dot "follow" the mouse, or is it a static dot that shows where a system is?
I know GD had x and y coordinate stuff, have you looked at the documentation for it?
While looking for help for you, I came across something I didn't know about PHP. SWFAction. Basically this is a small version of Flash. You could always take a static image and create your "movie" and capture mouse-clicks from that.
SWFAction
~Brett