Since MAC addresses are issued at the factory and do not change, they are often used for identifying devices on a network even if the IP address is unknown or has changed.
Multiple Network Interface = Multiple MACs
If a device has multiple network interfaces, it may have more than one single MAC address as the MAC is associated with a device's network interfaces, not the general device. In the case of cameras with multiple network connections (e.g., a camera with both a wired ethernet port and an integrated wireless radio), the device would have multiple MAC addresses.
Since the vast majority of cameras include only a single ethernet port, the MAC address could be/is often indirectly used to describe the entire camera.
Organizationally Unique Identifier
The first segment of a MAC address, typically six digits, is called the OUI, and each manufacturer is assigned one or more unique identifiers. For example, these are the OUIs of some common cameras manufacturers: