Social media giant Facebook is planning to secretly watch and record users through their webcams and smartphone cameras.

"According to a newly discovered patent, the company will use technology to see how facial expressions of users change when they come across different types of content on the site," Independent.co.uk reported on Friday. 

The patent document also suggests that the company would also analyse those images to see how users feel and later use that information to keep users on the site for longer.

For example, if you smiled looking at one of your friends pictures, Facebook's algorithm would use that information and display more pictures of that friend in your News Feed.

"Another example included in the patent application explains that if you looked away from your screen when a video of a kitten played, Facebook would stop showing similar type of videos in your Feed," the report noted. 

However, Facebook has not put these plans into action yet, and there's no guarantee that it ever would in future.