What lennon is saying is that the image posted from another website uses that site's bandwidth without putting any traffic through their site. Everytime someone views the graphic, the host site has to "push" the image to that computer. But they don't get the benefit of the vieweer actually coming to their website to view their content. 'Bout right, lennon?
If you copy the image to your computer (which is usually OK if it isn't trademarked) and you upload it to an image hosting site like
http://www.pictub.com, then the bandwidth is provided by pictub.