In the 7th grade, I made a 20-foot long mural of the Lewis and Clark Trail while we were studying that in history because I knew I wasn't going to be able to spit back the names and the dates and all that stuff on a test.
I discovered about 150 dots is the minimum number of dots to make a specific recognizable person. You can make something that looks like a head, with fewer dots, but you won't be able to give much information about who it is.