In recent years, digital signage is widely developed for DOOH advertising. Digital signage can be found in public areas such as shopping malls, airports, stations, and retail shops. The digital signage has an advantage over the traditional signage, which is able to show different multimedia content as requested by the advertiser. Most of the digital signage are designed with the display screen and computer equipment to deliver the message to the public . Instead of using static images, a variety of changeable content, such as video, audio, and animation are normally used to attract the audience's attention .