Twitter's algorithm prefers younger, slimmer and light-skinned faces

• Twitter's image-cropping algorithm prefers to show faces that are younger, slimmer and with light skin tone, a researcher has found.

• Bogdan Kulynyc won $3,500 in a contest organised by Twitter to find biases in its cropping algorithm.

• Earlier Twitter's own research found that the algorithm had a bias towards cropping out black faces.

• When two faces were in the same image users discovered, that the preview crop appeared to favour white faces, hiding the black faces until users clicked through.