Why don't some users add images when posting a question or answer? I believe that, at least for me, sometimes when the question is not very clear, the drawing helps to understand what you want. Do you think it is possible to insert an automatic alert between options, delete, flag, closed, etc.. where you ask to insert an image?
Asking for an image to illustrate the problem of an otherwise unclear question is fine.
Someone posting an answer should be allowed to decide for themselves if he/she wants to add an image. Don't harass people with comments to include images if you are not involved in either the question or the answer.