Yes, it is possiable, you can do it by flash, which is sortof an image, or you can have an input box surrounded by other images, so that it looks like an image. But for the typed text appearing in an image, I know you can somehow do that, I just don't know how myself, but it will probally take awhile to save the image, then upload etc... not to mention bandwidth and storage will go down faster.
I'm not sure where I can get one, but I hope I gave you, or someone else an idea to do this.
You can do this in php => www.php.net/image
never did it myself, but there are comments and examples which should help you out. You would want probably want to save the new image as a unique filename or something or use a database with the users comments and create new images everytim the page is called with the new images. Hope it helps