Every profession has things you can look up and things you just have to memorize. 540 people isn't much - can sports journalists recognize 540 athletes? Otherwise you'll be in situations where you don't have an opportunity to look them up (e.g., can't get a photo, no time, etc.), and you'll have many false negatives: If you don't know what they look like, you won't realize it's a member of Congress at the party with the coke.