To post a picture in a message, it needs to be somewhere on the internet, such as in your own personal webspace or on an online photo album. Most internet service providers (ISP's) give free webspace to subscribers.

To have the picture show up in your message, put in the URL of the actual picture, then highlight the url. While it is highlighted, click on the IMG button above the message frame. That will put IMG tags before and after the url of the picture, and make the picture itself show up in posts.

In your message, before you submit or preview it, you won't see the picture, but rather [img] tags before and after the complete url of your picture. But when you preview or submit, you then see your image.

Make sure your picture is not overly large. If it is, it needs to be resized at the original location before trying again to post it here.

For a size example:

This picture below is 300 pixels wide and 194 pixels high. This size, or a bit more or less, is a good size for posting pics in a message. Anything higher and wider than 500 pixels would be overly large and would need resizing.