Couple way to do it. Easiest way is linking from a photo hosting site. When you hit the "go advanced" button to post a rely. One of the icons above the text window looks like a picture with a tree, if you move your mouse over it, it will say "Insert Image" click on that and paste the link to the picture you want to post. Make sure the cursor is in a clear line before you click that icon. You can hit the "preview post" button to see if you did it correctly.