There are two ways to delete an image. Let's discuss one by one
$ openstack image delete <image>
Deletion of images is permanent and cannot be reversed. Only users with the appropriate permissions can delete images.
Select the appropriate project from the drop down menu at the top left.
On the Project tab, open the Compute tab and click Images category.
Select the images that you want to delete.
Click Delete Images.
Hope this will help you.