(To the best of my knowledge, GNU Appreciation Day is a figment of my imagination, and not an officially sanctioned event. There will be no sack races in Farmer Stallman’s field, and ribbons will not be given out for the Biggest Code Commit Grown From Seed. Not this year, anyway.)
By the way, in the spirit of things, that image isn’t governed by the Creative Commons non-commercial license. Apart from GNU’s usage requirements, use it however you’d like.