I need to draw a use case diagram of the system. but i am confused about its actors.
The system has functionality to automatically detect the fatigue (tiredness) of driver and alarm the driver as soon as it detects. User has nothing to do with this system. System will just take a live video of the driver and apply some algorithms to detect the fatigue. What are the use case involves in this system?
Well, if the driver notices the alarm, then he has something to do with the system, after all. There might be no direct interaction. You might still want to include the driver because he's what motivates your business case "notice tiredness alarm".
But I assume the system has a lot of other systems that it is connected to, i.e. where it receives data from (or reports back). Those external systems can be modeled as actors.