This is an ideal attribution
"Creative Commons 10th Birthday Celebration San Francisco" by tvol is licensed under CC BY 2.0
Because:
Title? "Creative Commons 10th Birthday Celebration San Francisco"
Author? "tvol" - linked to his profile page
Source? "Creative Commons 10th Birthday Celebration San Francisco" - linked to original Flickr page
License? "CC BY 2.0" - linked to license deed