Creating connection points for a PNG file

[Adrian Wooster <adrian wooster great-technology-company com>]

I have a comprehensive set of professional 3D PNG files of network
elements and have successfully created a simple sheet out of them - and
will happily share them once complete.

However, at the moment they are just insertable shapes with no
connection points assigned. Can anyone advise me on a simple way of
calculating where the connection points?

Regards,
   Adrian