Most likely you need to assign images for columns base, small and thumbnail in order for images to be reflected there.
You can do it from admin - export data, make changes in the file and import it back.
Also you can use other solution which have more flexible system of columns assigning. You can try to re-import via Store Manager for Magento application -
http://www.magentocommerce.com/magento-connect/store-manager-for-magento.html (free trial available for download)
Via Store Manager you can export products to the file, import it back and in the process of import assign your columns with images to columns for base, small and thumbnail images of database.
In any case trial version is free and you can give it a try. Let me know if it helped.