iRule to alert on hotlinking

Joe,

Thanks for the response. On my own I came up with

when HTTP_REQUEST {
                set refer_host [string tolower [URI::host [HTTP::header Referer]]]
                if { ( [matchclass [HTTP::uri] ends_with $::images] ) and ( not [matchclass $refer_host starts_with $::allowed_referers] ) } {
                log "Warning, Hotlinking detected from: $refer_host"
                }
}
 

I just had two questions,

1. If I add a data group list for allowed_referers, how are those input? FQDN? Just host? i.e. example.com, www.example.com, or http://www.example.com

2. what is the significance of "local 0"?