Form Post request + Image swapping

[Anon]

Hello, here's the situation I have in mind.

There is a form before you and it has a bunch of values. These values go over the limit of characters allowed for a GET request. Beside this form is an image/image placeholder.
Upon hitting submit or any button in genereal, I wish to send all this data to a image.php file, which constructs a png file on the fly. But I DO NOT WANT TO MOVE from the current page... infact I'd rather change the image source of the image/imageplaceholder to be the resultant data retrieved from the image.php file.

How would I simulate a HTML POST request like that and make it appear in the image src="" property of an image?
Is there a way?
Remember now.. Get requests don't work. So how does HTML send off the POST request? I know there is some data packet sent, but how do I alter that packet to be whatever I want?
Is an image src="" just a file reference or is it treated as a URL with a header etc..

I know I can't just append the image src with the form variables and respective values because it will blow up due to some sort of buffer overflow I'd imagine.

I know this is a bit out of the line of PHP but I've found these forums to be full of intelligent people.. so its my best bet.

[Anon]

What about putting the image in a IFRAME on the page and just change that URL when the user POST the information?

[Anon]

That would work in the newer browsers.. all I'd have to do is target the iframe from the form and boom there I go.

But, I think the older browsers wouldn't be able to see the thing at all. And I am forced to keep that in mind. This may be more of an j-applet problem but I'd rather explore all other paths before resorting to that.