On recent hardware with the T2 chip and new macOS - the camera is controlled in firmware and Apple makes it clear when it's engaged.
Look for a product like MicroSnitch to let you know when recording is happening - whether it's a legitimate program or a covert one.
As long as you are on El Capitan or newer, ...
Hands Off app has this feature:
Monitoring disk access
Applications present on your computer can freely read, store or erase information on your computer without your knowledge. Using Hands Off!, you can monitor and control disk access from all applications as to prevent them from obtaining confidential information, erasing your data or storing ...