Ever wonder how Netflix chooses the little thumbnail images that give you a peek at a show to help you decide if you want to watch it? Apparently there’s a lot more work that goes into these seemingly simple images that you could ever guess.

Quartz has a fascinating article on Netflix’s methodologies regarding these thumbnail images and how they affect viewers. The whole article is worth a read, but here’s a sampler:

How long does the average Netflix viewer look at a thumbnail image?

In 2014, the company conducted research that revealed users spend only about 1.8 seconds deciding if they want to watch something. It also found that most users pick what to click on by assessing the thumbnail images that Netflix presents to them upon logging in.

How does Netflix decide which images to use for each show/movie?

Netflix once used artwork from the studios for thumbnails. But that art wasn’t designed to be viewed in a stream, competing with other images. Today, Netflix designs its own images based on what it has found users are most likely to click on.

Through a series of A/B tests, the company realized that it could greatly widen a TV show or movie’s audience simply by changing those thumbnail images.

What kind of images work best with Netflix users?

While the brooding, aloof archetype is popular in TV characters, such emotions don’t necessarily entice Netflix users. Netflix users greatly prefer seeing a character with interesting facial expressions over one that’s “stoic or benign,”

[via Quartz]