BTC is really, really easy to recognize for humans, and it is completely NOT recognizable for machines (except for getting the whole BTC photos database with correct marks, but it isn't available for anyone).
BTC is very fast
Pictures database is really big (and it grows all the time), pictures are chosen randomly, then merged into one picture. BTC database is changing and rotating all the time.
Pictures in BTC are from many different websites (hundreds) existing in the web, there is NO possibility to get all the database.
