Display device capable of automatically adjusting displayed image and method thereof

A display device capable of automatically adjusting displayed image comprises a display device, a camera assembly, an image recognition device and a signal processor. The display device including a shell and a display panel partially exposed from the shell, wherein the display panel faces a first direction. The camera assembly obtains a first image with a first visual angle and obtain a second image with a second visual angle. The image recognition device generates a first instruction when the first image meets a first condition and generates a second instruction when the second image meets a second condition. The signal processor adjusts the display signal to conceal the displayed image according to the first instruction and to adjust the display signal to generate a reminder message on the displayed image according to the second instruction.