Your picture has to be somewhere on the web before you can post it in your message. We are all connected to Rich's server when we look at this, but we are not all connected to your computer, where the picture is. (Nor would you want us to be!) So first you'll need to upload the picture. Then, when it's on the web, you can put its *web* address in the same place you typed its address on your personal computer.
There are several places that will host your photos, up to a certain limit, for free. You can also host it on cornsnakes.com's server. Instead of hitting the IMG button, go to the Attach File button at the bottom. That will let you attach a file from your personal computer.