Spoiler alert:The man in the left upper corner and in the right lower corner is black and the two are white (head in the corner). One arm of the white man in left lower corner is longer. More help: First row, the black squares start in 1, 6, 11, 13, 15 ans 21.
(It can only be solved looking at the patterns, not at the numbers)
More help: First row, the black squares start in 1, 6, 11, 13, 15 ans 21.