Have you noticed that Netflix's video thumbnails follow a familiar pattern? That's no accident -- in fact, the streaming giant has developed a whole process for choosing those pictures. In a fresh blog post, the company has revealed details of a testing system that determines the artwork you're likely to see. Based on engagement and views, it can tell that you're more likely to click on images with faces, the fewer the better; it knows that villains are better choices for action movies and kids' shows, too. Netflix also knows which art tends to fare best in a given country, thanks in part to a system that automatically groups related images with different languages, effects and aspect ratios. It's aware if the Brazilian version of a picture is faring as well as the North American edition, for example.