Try leeching a photo from e.g. tomshardware.com, and post it elsewhere. The photo soon changes to 'property of toms hardware' or similar. Hmmm I think I'll leech a picture from Tom to show you.
@tmoic has a Content display mod, within the zip you will find getPhoto.asp & getImage.asp, those are forum independant and pretty self explanatory & commented files that will check the doman image is being served to and display a "No hotlinking" image if it is not your own.<
IIS > Properties from the domain > isapi filters > ADD > Browse > Apply > Restart IIS (not the server)....and so you can do this for every individual domain.
After the first Leech attempt IIS will give the leech blocker a priority.<