Screensavers

Screensavers were originally designed to protect computer monitors from phosphor burn-in. Early CRT monitors had problems with the same image being displayed for a long time. The phosphors used to make the pixels in the display would discolor the glass surface of the CRT when they would glow at a constant rate for a long period of time. This discoloration would then be visible as a faint image overlaying whatever else was displayed on the monitor.