Is it possible for Chrome extensions to monitor users without them knowing by taking screenshots and/or video?
There's an extension called Screencastify that allows you to record your screen. This particular extension (and many others) has a function that allows you to record your entire browser window. And here's the thing. When you set Screencastify to record the entire window, then go into Incognito mode, the browsing you do there gets recorded and saved. When you record the entire window, Chrome will show you a dialog box telling you that "Screencastify wants to share your screen," although it's not to hard to imagine a truly malicious extension bypassing this.
I personally think that this could be a privacy risk, as malicious developers and/or employers could secretly monitor Incognito and normal browsing activity without user knowledge.