An administrator has a need to delete an image that was used to create instances that are still running.
Platform9 Managed OpenStack - All Versions
OpenStack will not prevent deletion of an image which was used to create an instance that is still in an 'Active' state. However, if the image is deleted, it will not be possible to migrate the instance successfully. To prepare for deleting an image for which instances still exist that were created from it, it will be necessary to create a snapshot of each instance and recreate the instance using the snapshot. This will allow migration to function as expected.