This is so weird and frustrating. I tried denying access to paint.net but it wasn't in the list of apps that can be denied. I chose to deny all apps, and then when I quit and restarted paint.net it doesn't show the webcam image in the corner but it shows the symbol that was under it that alternates between a reload symbol and a pause symbol, and then when I reenable the camera in settings, it reappears in the corner. I guess it doesn't really affect my use of the program, I'm just using it as a cross stitch pattern so I don't care if there is a random image in the corner, but it's just so offputting to have my camera perpetually watching me, the little light is on, etc. Guess I'll be using the masking tape solution.