Check out Excel help for both "Background" and "watermark".

Background is under Format | Sheet. You may want to set the print area on
the worksheet since the background will show up multiple times.

"need excel recovery help" wrote:

I'm creating a family tree using Excel and wuold like to have a washed out
old pic as the background. In order to do this, I need all the grid lines to
show on top of this picture.

How do I put a picture behind everything including grid lines?

Thanks,
Rafy