Easiest way is to go to the page that holds the picture you want, hold down your mouse and highlight through the
entire web address, probably starts with
http://. Then right click your mouse and you get the option to "copy", left click that. Then come back to the reply box here, and right click the cursor in the reply box, then left click "paste", and if done properly, the link will appear in your reply, and the person can click on it to go to the page where the icture is. Try it!