First, the picture needs to be hosted somewhere on the internet. You can use your WDWMagic photo album for this, or an outside site such as Flickr, Photobucket, Webshots, Picassa Albums, etc. Once it's uploaded, right-click on the image and select "copy image location." Then, come back to the forums and click the "insert image" button (It looks like a little yellow box with a mountain on it). Paste the image link into the box that pops up.