Web camera teen
As a camera system's depth of field is greater for small image formats and is greater for lenses with a large f-number (small aperture), the systems used in webcams have a sufficiently large depth of field that the use of a fixed-focus lens does not impact image sharpness to a great extent.
Most models use simple, focal-free optics (fixed focus, factory-set for the usual distance from the monitor to which it is fastened to the user) or manual focus.
The video streams provided by webcams can be used for a number of purposes, each using appropriate software: Most modern webcams are capable of capturing arterial pulse rate by the use of a simple algorithmic trick.
Various lenses are available, the most common in consumer-grade webcams being a plastic lens that can be manually moved in and out to focus the camera.
Fixed-focus lenses, which have no provision for adjustment, are also available.
Typical interfaces used by articles marketed as a "webcam" are USB, Ethernet and IEEE 802.11 (denominated as IP camera). Various proprietary as well as free and open-source software is available to handle the UVC stream.
One could use Guvcview or GStreamer and GStreamer-based software to handle the UVC stream.