How should a proper hijab be?
If we post a non hijab or a hijab pictures on social media so is that ok ?

A woman is required to cover her head and whole body apart from the face and hands (palms). The clothing should not be tight and the colour of the clothes should not be such as to attract attention of the non mahram.

Posting pictures on social media, if with hijab, I'm not saying it is haraam but it's better to refrain from such from an akhlaqi perspective unless there is a need for it.