Image are not delete in magento until we delete the product in magento . So if we want to Delete all product images in magento use below steps.

1. Take backup of database first.
2. We need to empty two tables catalog_product_entity_media_gallery and catalog_product_entity_media_gallery_value.
3. open phpmyadmin and run following queries:

    SET FOREIGN_KEY_CHECKS = 0; Truncate table catalog_product_entity_media_gallery; SET FOREIGN_KEY_CHECKS = 1; 
    SET FOREIGN_KEY_CHECKS = 0; Truncate table catalog_product_entity_media_gallery_value; SET FOREIGN_KEY_CHECKS = 1; 

4. Remove all the files from "/media/catalog/product" folder
5. Clear all magento caches from admin panel