There is a way that works really well. Right click the game and go to Edit - Edit Metadata. On the left, go to Images. You will see all the images you have downloaded for the game. You can add images from your PC here too. Up in the top right the picture is labeled. "Box - 3D", "Advertisement Flyer - Front", "Arcade - Cabinet", and so on. Find the image you want to use. Right click the image and go to "Image Type" - "Box Front Images" - "Advertisement Flyer - Front". Then go through the rest of the images and find the one(s) already labeled "Advertisement Flyer - Front" and change the label to something else. I used "Advertisement Flyer - Back". There can be multiple pictures with the same label, so check them all. Then hit OK in the bottom left. It should now display the game with the picture you labeled "Advertisement Flyer - Front".