A way to allow uploading a signature

[dpaton05]

I have a spreadsheet that copies and pastes a signature that is stored on another sheet to the main sheet. The workbook will be protected and I wanted a way for users to update the signatures. I was thinking to add some kind of a control that would allow me to press a button and select a file. The file could then be copied to the other sheet by pressing a button. How would I go about this?