Twitter is learning first-hand about the challenges of eliminating racial bias in algorithms. The social network’s Liz Kelley said the company had “more analysis” to do after cryptographic engineer Tony Arcieri conducted an experiment suggesting Twitter’s algorithm was biased in prioritizing photos. When attaching photos of Barack Obama and Mitch McConnell to tweets, Twitter seemed to exclusively highlight McConnell’s face — Obama only popped up when Arcieri inverted the colors, making skin color a non-issue.

Others tried reversing photo and name orders to no avail. A higher-contrast smile did work, Intertheory’s Kim Sherrell found. Scientist Matt Blaze, meanwhile, noticed that the priority seemed to vary depending on the official Twitter app used. Tweetdeck was more neutral, for instance.