FACEBOOK has been secretly developing creepy technology which spies on people and automatically analyses their facial expressions.

The social network applied for a patent to capture pictures of a user through their smartphone.

4 CBI Insights found a patent granted in May which lets Facebook determine your emotion using pictures through your smartphone camera

The creepy designs, which date back to 2015, were discovered by software company CBI Insight, which has been analysing Mark Zuckerberg's "emotion technology".

Patent documents contain illustrations showing a person holding a smartphone with a camera taking a picture from which "emotion characteristics" like smiling or frowning are detected.

If the person appears to like what they're seeing, Facebook could place more of the same type of content in front of them.

4 A patent from 2015 reveals Facebook's plans to watch you read content on its social network and analyse your reaction

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4 It's most recent patent aims to add emotion to your messages based on typing speed and location

Patents don't always make it through to the end product- so it's not clear whether Facebook will bring out this new feature.

Researchers at CBI Insights warned that the plans could put a lot of people off using the service.

"On the one hand, they want to identify which content is most engaging and respond to audience’s reactions, on the other emotion-detection is technically difficult, not to mention a PR and ethical minefield," it wrote in a blogpost.

But that's not all.

Facebook appears to have tested out similar technology to work out which emoji to send to people using a selfie.

If you're smiling, it could automatically send a smiley face and vice versa.

4 Facebook founder Mark Zuckerberg in his home with wife Priscilla and baby Max Credit: FACEBOOK

Its most recent emotional patent - which was granted on 25 May this year - aims to tackle a dilemma many of us will have faced.

It can be difficult to make your text messages come across exactly as you mean them to, and sarcasm or jokes are often lost in translation - leading to some awkward conversations.

A new tool lets the social network to give your texts more feeling - so they won't be misconstrued.

The system picks up data from the keyboard, mouse, touchpad, touchscreen to detect typing speed and how hard the keys are pressed.

Facebook will accordingly change the text font and size, before shaping to make it more emotive and relevant to your mood.

Facebook said that it does not currently offer tools to detect emotion.

If you want to check what Facebook sees and shares about you, check out its privacy policy here.

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