Cisco IOS Image Resilience is part of hardening and securing your Cisco IOS router.
The IOS image or/and the startup configuration can be tampered or corrupted and during downtime failure, the recovery procedure, to bring up the router, can take sometime. You have to load a new IOS image and then a find and load new config file.
In order to save all that and to ensure that during a downtime failure, your router, will be able to recover at a minimum time an IOS Resilience feature has introduced since IOS 12.3(8)T.
The feature maintains a secure working copy of the router image and the startup configuration at all times.
The configuration is made in the global configuration mode:
Router(config)# secure boot-image
to maintain and secure IOS image
Router(config)# secure boot-config
to maintain and secure startup config
to view the configured setting type: Router# show secure bootset