Just because a person is short doesn't mean they deserve to be discriminated against. There's no natural way for a short person to become taller (considering if they grew to their maximum height already). No matter what, a short person is short, and a tall person is tall. They both have their pros and cons. There's really no reason for someone who is short to be bullied in terms of their height.
(By the way, the picture you posted is a horrible example considering it's only a child who can be in Grade 3 or 4 standing near adolescents who can be in high school.)