<img src="http://www.econ2.uni-bonn.de/schweinzer/pix/Diana.Rigg.01.jpg">
Go to almost any any web page and right click on the picture you want to post. Select PROPERTIES and read the URL of the picture. Substitute that for the URL of this picture, which I highlighted in blue.
et voila
Me? I cheat and use Frontpage then copy the code between <body> and </body> and paste it into the posting window in FR.