Usually done with several duplicate slides. Make one picture bigger on each
and have a mouseover hyperlink to jump to the relevant slide, You can also
arrange an invisible area on the target slide to hyperlink back.

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John Wilson
Microsoft Certified Office Specialist
http://www.technologytrish.co.uk/ppttipshome.html
> How to enlarge individual small pictures (thumbnails) on a slide into large
> ones during slideshow?
> I am sure I have seen it done in presentations when the mouse arrow hovers
> over the thumbnail and the picture zooms in.
>
> Any advice would be greatly appreciated.