Snoop Catcher

Snoop Catcher is a straightforward application, developed for Mac computers, that acts as a guardian by automatically taking snapshots of anyone trying to use your machine.
It doesn't require advanced computer skills, so it has a fast learning curve.

Its GUI is represented by a small window, from which you have to select the destination folder for your snapshots. Other basic options can be found on the top menu bar, but those are more common.

It must be said from the start that it's a one-function application. There are no advanced options for you to configure, so advanced computer skills are not required. To start using it, you only have to run the application and once the main window pops up, select the destination folder for the snapshots. The app will take a snapshot each time you start your computer, so you can see if someone secretly accessed your PC.

It must be mentioned that the app does flash and makes sound alerts when it takes snapshots, as it's against the App Store policy to secretly take photos. Therefore, maybe it's not the best solution for you to catch privacy intruders.