1. A digital photo frame comprising; an image memory configured for storing a display image; a display device configured for reading and displaying the display image; an infrared sensor configured for detecting infrared light, generating a first detecting signal when the infrared light is detected, and generating a second detecting signal when the detected infrared light is no longer detectable; and a camera control circuit comprising a reference image therein, wherein the digital photo frame is in a standby mode when no detecting signals are generated by the infrared sensor; the camera control circuit generates an instant image and compares the instant image with the reference image when the first detecting signal is generated; and the digital photo frame is configured to switch to operating in a monitor mode or a display mode from the standby mode according to the comparing result when the infrared light is detected.