A computer screen shadow problem can result from display hardware issues, problems with the cable connecting the device, setting-related problems, or a graphics driver problem. Start with checking the cable connected to the monitor and making sure everything is fine there. Turn off the computer and reboot it. Reset the graphics driver by pressing Windows, Ctrl, Shift, and B keys simultaneously. If you have an additional external monitor, try switching cables or connecting the monitor to another computer. In case of a laptop, you can check your internal display against an external one. The shadow that remains in one place and does not show up in screenshots is likely caused by the physical screen itself.