Watermarking.

Watermarking is a two step process.
The information is filled into the Excel Spreadsheet.
watermarking is then placed on the spreadsheet seperately and is then
printable
I am not aware of any process that will place a watermarked pic on your
spreadsheet during the data entry process.
If you are interested in the website, enter watermarking in the search for
box under discussions in Excel General Questions.
http://www.xldynamic.com/source/xld.xlFAQ0005.html