AVI ASHER-SCHAPIRO SOCIAL media giant Twitter said on Monday it would investigate its image-cropping function that users complained favored white faces over black. The image preview function of Twitter's mobile app automatically crops pictures that are too big to fit on the screen and selects which parts of the image to display and cut off. 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 alongside Republican Senate Leader Mitch McConnell. "Twitter is…