How to create my own bingo card generator

Functionally, it would be very similar to this site:
http://bighugelabs.com/mosaic.php

I'd like to have a bingo card template (5 x 5 card) and people can fill in images for each of the squares, and the images will all be from a select group that I have already pre-determined.

I've barely done any PHP programming at all, but I think I can do all the easy stuff. The one thing I'm not sure how to do would be to actually generate the image at the end and create a jpg from it. I basically want the users to be able to choose 25 images to fill in each of the squares and then when they hit 'submit', it will give them an image of their bingo card which has each of the squares filled in with what they specified. I want to know if this portion would be hard for a newbie to learn or if it is doable.

Thanks in advance.

Since it's only 25 cards possibilities, just use actual JPEGs. Don't make PHP do extra processing for such a small random load. That's just going to weigh down the processing.