Every player that wins a game on the Map of the Month gets awarded that month's MOTM badge. As well, each win on the Map of the Month is worth points in a tally to determine the overall winner that month. Here's the breakdown:
6 human MOTM win = 50 tally points, plus the gold badge
5 human MOTM win = 30 tally points, plus the silver badge
4 human MOTM win = 20 tally points, plus the silver badge
3 human MOTM win = 10 tally points, plus the badge
2 human MOTM win = 5 tally points, plus the badge
The MOTM page has a listing of wins for each player, with 6 human wins first, then 5, then 4, etc.
The player who has gained the most tally points at the end of the month is the winner of the Map of the Month.