Remove Category images – Create Theme

Is there a way of removing a image from a particular category and a particular product? I have a number of categories and individual products that don't have images and I would like to remove them from the display. I found some code online and that suggested adding: .category .post-image ! { Display: none; } At the bottom of the css style but this didn't do anything. In addition to the above I would also like to know how I can add a widget area in the footer. Can you help.