Go advanced, manage attachments, find your pic, attach. If it's not the correct requirements, resize it. Or host it somewhere else and link it here, like holabuster tried to tell you.
Your a tard. This is such a self explanatory question that all you would have to do is just LOOK. Coming to a 150 posts and you have yet to know this, is beyond any explanation. Advanced is next to your Quick Reply button.. Hit manage attachments and go from there.