help with images

First of all please excuse my ignorance if anything that I ask here is impossible or a common question, I have searched but not found the answer. I'm working with composite images which at the moment are dynamically produced and set in html layers. The problem is that I want the user to be able to save the image. This is not possible at the moment because the browser only sees one part of the composite image. Is there any way that php4 can 'flatten' an image to preferably jpeg and then show it on the screen. Thanks for any guidance, Gav