A web camera includes an image sensor, which takes an external image; a sensor interface, which is connected to the mage sensor to receive and convert the image taken by the image sensor into digital image data; at least one compression module, which is connected to the sensor interface to receive and compress the digital image data into compressed image data; and a USB interface, which is connected to the compression module to output the compressed image data to a host device having a USB interface port, such as a computer and a USB OTG device, for storage, playing back and other applications.