No, you can only select from the ones they've included. Adding an image upload function would also require the implementation of a vetting system, and the explanation is that there wasn't time to get that done this year (but maybe in future games).
It's unfortunate because adding custom graphics to the game is a cool idea, but seeing what some people do in 2K with a vetting system in place, I can understand not wanting to allow everyone free reign to upload anything and everything.
2K's system has been pretty good at keeping out nudity, gore, that kinda stuff, but you still see politically charged garbage, photos of Rachel, photos of people that they probably didn't authorise the usage of (some 2K Pro-Am team we once played appeared to be using a photo of a girl one of them had a crush on), and other questionable or stupid images. The ability to upload custom images is a great feature, but some users definitely abuse the privilege.
Finally took the time to copy my screenshots to my computer to post. I worked on 1 court for myself and 4 retro courts. Obviously, in the demo I don't have all the pieces I need yet to finish the courts (logos)
What is annoying is that one of the locations where you can place logos is called "Arena Name" but you can't put text in the Arena Name area where you'd expect an Arena Name to be
It should be. 8 reminded me a little of some of the fonts they've used at times, which is why I went with it. If there's a better option, I'll switch it up.