From The Apple Wiki
The LcdUTest Icon (Before iOS 6)
The LcdUTest Icon (iOS 6 and up)

LcdUTest is a SwitchBoard application used to test different aspects of the display. This application was redesigned for factory firmwares on 6.x and up, switching away from the purple tinted icon to a newer, more vibrant one instead.

Upon opening the app, you are presented with a bright white screen. Double tapping the screen presents you with a "Setup Options" panel, where you can adjust various details of the screen. This panel also allows you to choose between three different sets of images indefinitely; FATP, IQC, and OTHER. Using volume up and down or tapping the screen allows you to choose between various provided images. Holding down the home button brings up a menu which allows you to cancel, quit, or shutdown the device.

The Contents of This App