Social media giant Twitter said Monday it would investigate its image-cropping function after users complained it favored white faces over Black ones.

The image preview feature of Twitter's mobile app automatically crops pictures that are too big to fit on the screen, selecting which parts of the image to display and which to conceal.

Prompted by a graduate student who found an image he was posting cropped out the face of a Black colleague, a San Francisco-based programmer found Twitter's system would crop out images of President Barack Obama when posted together with images of Republican Senate Leader Mitch McConnell.