I want to create a square photo collage - but where can I do it?

[2jamsandwiches]

I thought this would be simple - I want to make a square collage with square pictures (4x4 or 5x5). But I can't find anywhere that allows me to do it - photobox etc. just seem to do rectangular prints. Has anyone found anywhere that does this?
Thanks!

thank you!

but what I was hoping to do was to be able to print a whole collection of square pics on one sheet, if you see what I mean. So not a collage made up of things stuck together, but things all printed together, do you see what I mean? I've still not found where I can do it, is bizarre how difficult it is!