The average web user doesn’t know much about search optimization and will usually enter a person’s name as expected (“kevin leery”) with no quotes or spaces. This makes it very important to tag and label your Flickr photos in the best way possible to ensure that they are found by users searching the service. Kevin McShane proposes best practices for tagging people in photos to maximize search result relevance.
By following these best practices your Flickr photos have the best chance at showing up high in the search results regardless of search method.
This article is pulled from an incredibly helpful post by Kevin McShane in the Flickr Help Forums.