iWork (numbers) help please

Ive setup a spreadsheet in numbers that contains all the films ive watched this year including cover art, ratings and description. However i just copied and pasted in the cover art which i thought would be fine but now my 40 or so films has made the file size 30mb+ due to the cover art, ive seen there are options to reduce file size but none of them work if the pictures have been pasted into the cell and are applied as a cell background, is there a way to reduce the file size?