Tech giants Apple have acquired Emotient, a San Diego-based start-up which uses artificial intelligence software to analyse facial expressions that can be used by advertisers to assess viewer reactions.

On its website, Emotient is described as “the leader in emotion detection and sentiment analysis, part of a neuromarketing wave that is driving a quantum leap in customer understanding. Our services quantify emotional response, leading to insights and actions that improves your products and how you market them.”

In May 2015, Emotient announced that a team of people, found through a crowdsourcing website, were used to train its machine-learning system by collecting and labeling the emotions of 100,000 facial images a day.

Here’s a demonstration video from the website:

This exercise was to teach the computers to better recognise different expressions. Blog posts on Emotient’s website, which have since been removed following Apple’s acquisition, described how the team “harvests faces” to create “emotion-aware machines”.