At the bottom of the post form there will be an “Image File Attachment” option, just hit the browse button and pick the picture you wish to add (please note that if the picture is to big you will not be able to attach it). Unfortunately you can only add one picture per post, and it will show up as an attachment link. If you want to add more than one picture you can post it in a reply to your original thread, but please be reasonable with how many pictures you post.