Answer:
There are several factor that influences how people define their personal body image. First, their auto perception, how they themselves plays an important rule to define self body image, if people see themselves in a negative way, their body image is gonna be wrong for them. So, from this we can deduct that body image is also defined by the self-esteem, how people emotionally see themselves, which is also important, because that's why people in obese condition or overweighted, they don't see any problem, because they see themselves good.
On the other hand, the environment influence the personal body image, but not necessarily affects how people perceive their body image, that perception is always from an emotional perspective, because we tend to be subjective people, we are subjects.
Therefore, self-esteem and auto-perception are two crucial factor.