A simple corner bracket for 5mm foam core board. I wanted something a little better for taking pictures but didn't want to spend a ton of money. I picked up the foam core boards from walmart for a couple of dollars each and it did the trick I needed.
No supports needed.
If you are looking for a seamless background, I also designed a bracket that fits perfect with your average poster board.
https://www.printables.com/model/1216782-seamless-background-supports-for-poster-board
The author marked this model as their own original creation.