Sixth of the series "The Four Dogs" I just found it out at the amazing The Mad Hatters. Duncanr is the responsible for the photo:
There are four black dogs at the left and three at the right side because the fourth is in charge of dragging the boat. The two browns in the center are clearly sad and angry for their partners were left in danger because of lack of space at the boat. So we have twelve dogs divided in three: four dogs as always.