Forum Moderators: phranque
The second option isn't generally possible, because the "replacement object" would have to be an HTML file. However, since the image is being included on the hotlinker's page by an <img src="xyz.gif"> tag, the browser won't accept an HTML page when it's looking for an image.
Either make a replacement image that looks OK when scaled to any reasonable size in portrait or landscape mode and shows the URL of your site, or simply deny access with a 403-Forbidden and be done with it.
The secondary problem is that the URL in the replacement image won't be clickable -- The viewer will have to type it in.
Jim