When you're posting a reply, above the message window there are a few icons. One is a yellow square that looks like it has a mountain and a sun on it. Click that button and insert the link to where you have the picture hosted. You must have the picture hosted on a website such as photobucket.com to do this. If you're a high-bandwidth member, you can scroll down and click on the manage attachments button to attach an image from your computer.