Put the picture in a waterproof plastic bag, seal the bag, and then place it vertically in the cup with the plastic bag. You'll see the picture disappear.
This is because there is air in the plastic bag containing the picture, and the light first enters the water. Then, if the angle of light entering the air is too large, it does not refract but produces a reflection, which is called "total internal reflection", causing the picture to disappear.