The 'browse existing images' functionality would have to be built, just like the one that the BC admin UI uses had to be built.
There may be a way to re-use that one on the front end, but I suspect it's strongly coupled to the frameworks in use.
Thanks for your answer, Robert.
I would have thought this functionality would be pretty fundamental for creating a user-friendly environment for the user.
I suppose when you say that it's 'strongly coupled to the frameworks in use' that it's not an easy task?
Yes. For starters, it's difficult just to get the list of images in a folder from the frontend.