You can put anything you want into a Photoshop document and get a print made. I have sent scans of artwork to have prints made. So... make your collage and make a neat gift for your friend!
If you have a fast connection, or can get to one for uploading, I recommend making your file size twice the minimum requirement, of 1600x1200 pixels or 5.5 MB.
A file of 3200x2400 pixels will give you a 22 MB file, but the quality will be better.
Or... you could go for something in between like, 2400x1800 pixels (12.4 MB).