OK... I don't know where I got "single event handler from," that obviously wouldn't be true, but it would still be simpler than having each pixel be a separate HTML form....
Let me actually see if I can come up with a POC first, at least for the canvas and javascript. Realistically, since it's just GET requests that don't need authentication, I shouldn't even need laarc running, I can just send the same requests by AJAX.