[dm8]

I didn't see different poster for same movie although I'm not a caucasian. Maybe it's just not your ethnicity but also your previous viewing habits. For example, if you watched lot of movies with hispanic or Indian or african-american actors then you might get those posters to incentivize you to watch more.

I'm pretty sure they have exhaustive feature set (not just demographic information) in their model to select the cover poster for user.

[hactually]

It's all about engaging. It's actual leveraging the biases of the individual rather than Netflix. You're being racist, not netflix which is kinda funny.

There's data points to indicate you're more likely to watch X if they show A,B,C title cards. When you do, that reinforces that link. In aggregate it feeds data points to Netflix that lets them A/B test the needed graphics.

Customer biases driving biases/business decisions.