The application provides a network camera, a video monitoring system and a method. The network camera comprises: an image sensor, a processor, a memory and a network communication interface; the processor is configured for matching a current image acquired by the image sensor with an image stored in a second storage unit of the memory, so as to obtain a similarity value representing a matching result, and storing an image satisfying a similarity condition in another storage unit of the network camera, reducing the difficulty of image comparison and improving the accuracy of the comparison result.