If it doesn't work first time with sunglasses then you use the "Improve Matching...

rogerbinns on Oct 2, 2013 | parent | context | favorite | on: Fingerprints are Usernames, not Passwords

If it doesn't work first time with sunglasses then you use the "Improve Matching" to take a pic of you wearing sunglasses. They don't want identical pics of you - they want pics of how you vary. (Same story with facial hair etc)