This class of camera typically is a c-mount type and outputs the image direct to a computer monitor.  This class of camera is superb for teaching applications.

 The main unusual characteristics of these cameras are:

• Extremely fast refresh rates producing superb live images
• Very high resolutions in live mode
• No computer needed
• Ability to freeze the image
• Some models have overlays such as crosshairs on top of the live image
• Some models have builkt in memory card writers so images can be captured.
• Many models have absolutely superb colour reproduction

Because these cameras are designed primarily for live image capture the sensor size is usually limited to a maximum of 2MP, which i perfectly high enough for most purposes.

These cameras cost much more than the equivalent USB version simply because they are rarer, more complex, have a higher specification chip and are built in much, much lower quantities.