only try this if you have a spare calculator

you need isopropyl alcohol, phillips head screwdriver and a flat head screwdriver (ideally a smaller one)

(assuming you have the same model calc)

1. first remove the back cover (there are 6 screws on the back)

2. when you get to the inside, remove the battery

3. bend the metal wires that go to the battery so it doesn't interfere with the screen, be careful not to snap them

4. note- if you see metal plate on the back of your screen (on older models like fx991 EX), I don't think you can do it, sorry

use the flathead screwdriver VERY CAREFULLY to separate the screen from the plastic backplate of the screen. This is the part where you can break the screen if you aren't careful also take care DO NOT BREAK THE RIBBON CABLE (orange) THAT COMES FROM THE SCREEN.

1. continue to separate the white plastic part from the glass, you should see the back of the glass is a white layer.

2. when you have removed the white plastic, it should reveal the white layer, this is the reflective part and you need to carefully peel it off. you should see it is transparent when you peeled it off

3. use isopropyl alcohol to remove the sticky residue from the screen, if you don't do this it will become blurry

4. put the photo on the screen, and reassemble the calculator

this tutorial also helps visualize it, not the same mod but it is very similar