your pictures must be stored on a public server. some internet providers give free server space w/your account. you can also use photobucket.com. it's free & easy to use.
after you have your pictures stored, click on the "Img" button above the message box. then insert the URL of the pic & then click the "Img" button again. if you need more instructions on how to upload to photobucket or your provider, pm me.