I ve seen webpages where the images have been hotlinked stolen from others and the image isnt the one they expected. You could really give the thief a big shock depending how far you want to go ;-)
At the very least you can change the picture to an annnouncement about how crap his website is and how he is a thief.
Im not sure about dreamweaver but as a novice user you could easily upload images to your webspace under well defined names to use in making your webpages. For example
http://any_eircomwebspace.net/flower.jpg
The crucial part is you get to decide the name of the file being hotlinked when you upload it.
Then once you discover a particular image is being stolen, you delete the stored image and then proceed to reupload a vastly different image under the same name which the thief is hotlinking to unawares its been changed.
Repair your own website by having your own flower image renamed in your source code then surf to the thiefs website and watch your own handiwork. You control what his website shows and its his own fault.
In such a case be happy to provide the bandwidth for his own downfall.
So in plain english summary , discover which image is hotlinked then reupload a new image of the same name but with different content.