how, where, when ... and just for the interest sake, why?
a few more details in your question will enable us to provide a useful
answer.

It's a company logo placed in several locations in an excel worksheet
and I may have to change/replace the picture. My thought was to have a
picture as an external file to link to a spreadsheet. Then if I
change/replace the picture with the same name, it will automatically
update the spreadsheet hopefully.
Hope this helps.