The USB camera is used as the front device of the image acquisition. The host computer is a PC for the detection system. Aiming at low resolution of USB camera, the super-resolution image reconstruction method based on sparse representation is used to overcome the low resolution for the low-cost imaging sensor and improve the image resolution. In order to reduce the influence due to shooting light, angle, etc., visual keywords are used for image matching to improve the robustness of the system. The experiment proves that the system is simple in structure and easy to operate, and the detection accuracy of the system can reach 98.67%.