crying is expression while not crying is usually concealment.

our ability to read human emotions is just right.

if we were able to tell the photoshoped picture was sad, then everyone would be in everyone's business.

Concealment of emotion and sensitivity to emotional states are complementary skills in social interaction. We ever strive (consciously or not) to become more masterful in concealment while being more sensitive to what others try to conceal. We generally do that because it represents an advantage and therefore a selective pressure.