If your dog isn't microchipped you will need a passport sized photo of he dog stuck in the agility record book, as the measurers have to sign over it to attest that it is the same dog.
If it is microchipped they will scan it.
When my Zig was measured, she was microchipped, but it was then I found the chip had failed! Getting the photographer at the show to do the photo was really quite costly, so go prepared.