This rule is also a generalisation, pictures can also include asian's hispanic's etc. This practise of included a large demographic of people could have been the indirect or direct result of civil rights movements and lawsuits.
Ex 2. The White Black Handicap Rule was probably the result of court action, and now schools need to include all ethnicities in its representations of people.
John: So I went to my little borthers school yesterday to pick him up and boy it that place weird.
John: There were cartoon pictures of people all over the place and they all had a white, a black, and a handicap, every last one
Mike:Oh, thats just the WBHR, guess they had a problem with racist 5 year olds they needed to fix haha.