A new HD webcam's image only updates one or two times per second.

 The USB 2.0 port has insufficient bandwidth to support a high-definition webcam that can update 30 frames per second. USB 2.0 has a maximum theoretical bandwidth of 480 Mbps, which may not be enough for HD video streaming. The user should try using a USB 3.0 port or a Thunderbolt connector, which have higher bandwidths and can support HD webcams. The Thunderbolt connector is compatible with USB devices, so it is not the cause of the issue. The VGA cable and the STP cable are not related to the webcam, as they are used for video output and network connection respectively.