The ESP Game dataset (Von Ahn and Dabbish, 2004) was famously collected as a "game with a purpose", in which two players must independently and rapidly agree on a correct word label for randomly selected images.
images in the ESP dataset do not make a distinction between objects in the foreground and in the background, or between the relative size of the objects (tags for images are provided in a random order, so the top tag is not necessarily the best one).