Thank you for your reply, Doreen.
At least I now know that I wasn't just missing something that everyone else knew about!
I do think it's a shame that the images are so small - it's almost impossible to see what the image is of in some cases at that size and when presented with a choice of images to click on, I'm sure most people will go for the ones where they can see what the design is about! On my blog, I put all the GCU ones together at the beginning because I had the feeling that if they were mixed in with the Zazzle ones, they'd mostly have been overlooked completely!
Anyway, maybe this is a further refinement that the GCU staff could look into at some point to put GCU artists/designers on an equal footing with the Zazzlers?