Forgive me if I'm overlooking something really obvious, but if you wanted to hotlink to an image, would you not point the entry in your TOC directly to "../Images/frontispiece.png" and not out to "../Text/Section003.xhtml#frontispiece.png" which implies an id or name="frontispiece.png" attached to a tag somewhere in the xhtml of Section003?
Or if by hotlinking, you mean you just want to have it jump directly to that part of Section003 where the image is shown, and not just to the image file itself, then you'll be wanting to add said id="frontispiece" to either the <img> or <div> tag immediately preceding, and have your TOC code as "../Text/Section003.xhtml#frontispiece" or whatever you choose to id it as.
Hope this helps.