An exemplary digital photo frame includes 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, generating a second detecting signal when the detected infrared light is no longer detectable, and a camera control circuit including a reference image therein. The camera control circuit generates an instant image and compares the instant image with the reference image when the first detecting signal is generated. The digital photo frame is configured to operate in a monitor mode or a display mode according to a comparing result when the infrared light is detected.