From Excel Help
"In Excel, you can use a picture as a sheet background for display purposes
only. A sheet background is not printed and is not retained in an individual
worksheet or in an item that you save as a Web page. It is retained only when
you publish an entire workbook as a Web page.

Important Because a sheet background is not printed, it cannot be used as a
watermark. You can, however, mimic a watermark by inserting a graphic in a
header or footer."

Look under "Mimic a watermark in Excel" for how to insert a watermark.
"Euan Ritchie" wrote:

Is it possible to print a displayed background which is included in a
spreadsheet?