I'm going to use brickshelf as an example.
This is the example image.
Here is the image URL:
http://www.brickshelf.com/gallery/DYuha ... trod01.jpg
Copy the image URL and paste it between image tags:
To post your image, it needs to be from an internet source, i.e., an image host. And if you do that, for the love of all that lives, RESIZE YOUR PICTURES FIRST.