The thumbnails are always changing on Netflix because you're being tested

Recently I started re-watching Parks and Recreation on Netflix, and about halfway through the series I noticed something strange. The thumbnail for the show had changed from a confident, glowing picture of Amy Poehler's Leslie Knope — the show's lead — to a photo of Chris Pratt in crutches. But the thumbnail hadn't changed for my colleague Helen Havlak, who pointed out to me that she was still seeing Knope's face.

I already knew Netflix constantly changed thumbnails, and I assumed it was trying to figure out which were most popular. Today, Netflix confirmed that suspicion, and explained how it A / B tests thumbnails in two blog posts.

@chillmage my Netflix thumbnail is all Knope so maybe there is sneaky demographic targeting at work

— Helen Havlak (@anotherhelen) April 15, 2016

Netflix writes that the artwork on its content has the biggest influence on what people choose to watch — capturing "82 percent of their focus while browsing Netflix." Well, yeah, that seems obvious; Netflix is a giant carousel of image thumbnails! But Netflix writes that the window for getting someone's attention is pretty short: users spend an average of just under 2 seconds looking at each show or film they come across. So Netflix took these findings and decided to build a system that harnesses the judgements people are able to make in that span of time.

There's definitely some sneaky demographic targeting going on. Netflix calls differences in engagement "regional nuance," but what it's really talking about is aggregation of unconscious bias. The company found that thumbnails for Sense 8 differed in popularity between Germany, the US, the UK, and Brazil, and the difference in Netflix's examples appear to be driven at least partially by racial identity. Netflix also says it identified several other winning strategies:

• Show close-ups of emotionally expressive faces
• Show people villains instead of heroes
• Don't show more than three characters

"Over the last few years, we have worked hard to learn how a winning combination of technology and creative helps members discover stories they will enjoy faster," Netflix writes. "It is clear that an image can move people in powerful ways." That all sounds pretty innocuous, until you realize that soon you might click on the latest Adam Sandler film before you realize it's a mistake.

Netflix's plan for world domination

• SourceThe Netflix Tech Blog Netflix
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