Is it permissible to follow male and female colleagues from school on Twitter with the aim of getting to know what they write, and is there sin upon the one who follows if personal or forbidden pictures of the female followers appear?

The basic ruling is that it is permissible to follow posts on Twitter unless they contain something objectionable. Personal communication between the sexes via social media networks carries obvious risks, unless it adheres to the Sharia guidelines, such as ensuring safety from fitna (temptation), absence of lust, presence of a genuine need to the extent required, refraining from lewd speech, women not posting their pictures, and not looking at their faces. If following female colleagues' articles leads to prohibited communication, then it is not permissible, unless there is a valid need. The prohibition and sin are confirmed if a woman posts her personal picture or a forbidden picture, due to the impermissibility of looking at women's faces, even without lust.