Use the boot system flash command to tell yuour box where to get its image on boot-up.
SLARP=Serial Line Address Resolution Protocol
People use it to set-up rourters remotely. For example you send your customer an unconfigured router from local stock and he plugs it into the leased line at his premises. The upstream router from his is configured as a staging router and a an autoinstall can take place without the customer ever logging into the router.
Autoinstall of cisco routers