Right button-click an image (make sure it's in the size you want to display) For IE select "properties" in the popup menu. You can then highlight and copy the URL and place between image codes, then post. It's that simple.

For Firefox, on right-click you choose "copy image location" and then paste between image codes.

Keep in mind if you do this on a thumbnail image, it's going to display the thumbnail. If you want to show it in full size, then view it in full size before copying the URL.