If you inserted the background image through the Format > Background > Fill
Effects dialog, then go to Tools > Options > Print and uncheck the
"Background colors and images" box.
However, it's more likely that you inserted the image either with the
Watermark feature or by inserting a picture anchored in the header (which is
really the same thing). In that case, go to Tools > Options > Print and
uncheck the "Drawing objects" box. Note that this option will suppress
printing of _all_ graphics that aren't in line with text, as well as text
boxes (Insert > Text Box).