That's great, and if I didn't already have my own hosting server, I'd be delighted with this. One question, though... will the end result be the same in terms of what other people browsing the forum see? In other words, will the image posted using the form appear as a thumbnail in the message, and then when you click it, you get spammed by pop-up advertisements even before you can see the enlarged version of the image?
I'm not intending this message to be offensive, just sharing my experiences of using ImageShack.