The best way to post pictures is to create an account with photobucket.com (or similar) - its free and easy to do.
When you have done this, go to the 'upload images' window, hit browse and find the photo that you have saved on your pc. When the image has been uploaded, you can select it and hit the 'generate HTML and IMG code' button at the bottom of the page. Copy the html code from the IMG images window and paste it into your message window.
At least that is one way of doing it.