The USB device specification limits reliable data transfers over a devices USB cable to around 5 meters or about 16 feet for High-Speed devices. The distance is a bit less for Low-Speed devices like keyboards and mice. An Active USB repeater extension cable can extend the webcam's distance considerably.
Active Repeater cables are available up to 100 feet. Some of the shorter one's simply reamplify and reclock the 5 volt signal coming from your Mac computer's port to extend a webcam (or any other USB device's) range. However for longer distances, you should look for USB extension cables that include a separate power-supply to adequately and reliably boost the signal. Extending a webcam with ordinary USB A-to-B extender cables will likely result in the device disappearing off the USB bus and possibly causing your video application to lock-up or crash.
For some, extending their Mac webcam via Ethernet cabling is preferred for ranges up to 300 feet. Above you see a pair of USB transceivers: One for your Macintosh's USB-A port, and the other end with a power-supply input and USB-B female socket to plug your web camera into.
Lastly, note extending SuperSpeed USB 3.0 devices (not webcams) required different, USB3 certified cabling and extenders. That's not an issue for Mac webcam users since NO web cameras made currently require nor operate at USB 3.0 speeds. All Apple-friendly UVC compatible webcams are USB 2.0 speed devices.