Two ways to do it.
First off, you have to realize that the image has to be on a server on the internet. It has to be downloaded to some/any server. It has to be hosted.
If it's already on the Internet, it real easy, just click on the little image box, the Yellow one, with the mountain on it, and enter the image location, the URL.
Now, chances are, you do not already have the image hosted on the internet. In that case, you can host it on Crappie.com by doing the following:
When you post or create a new thread do this (click) - Go Advanced, Attach files, Manage Attachments, (when you click on Manage Attachments, it'll walk you through downloading your images) then you can include the picture in a post using the URL (internet address) mentioned on the page.
I know, a little confusing, but go through the motions, you should be able to follow along. Good luck.