It is a known issue that a hacker access the webcam and mic on your device without your consent and awareness. You can take the help of a tape but it can’t be considered a wise solution. An ex-NSA hacker has created an anti spying tool for OS X which alerts you when an application tries to access the FaceTime camera and mic.

Source: Don’t Put Tape On Your Webcam, This Free App Alerts You When Someone Hacks It