Photographing flat art is a bit of a science in itself. Reflections are diffcult.

Paper prints - you could use a vacuum easel to hold them flat, or you can crop them just a hair and use magnetic rulers to hold the edges down. Light the pictures from both sides, at a 45 degree angle, and place the camera above the top of the lights. If you have polarized light sources, that will help in creating a good copy.

You could get a copy stand too, which has the camera mount built in, and the lights, and a flat surface for the items you photograph.

If you weigh down the prints with glass, reflections will become an issue. You might be able to eliminate some of that by using a polarizing filter on the camera lens, but it's going to be difficult at best.