If the image is at the beginning of the topic, or all by
itself in a reference topic, you can put "#" (minus the quotes) as
the link for each hotspot.
If the image is larger than the viewing window, it may jump
to the top, but only if the user clicks the link.
I've tried wz_tooltips and like it. I agree with Leon, it
will take some time for the first image but might go faster
subsequently.
Harvey