before proceeding past these fuzzy lines select all zebras careful tho — one zebra may hide behind another
Image: Paul Maritz (detail), CC BY-SA 3.0 , via Wikimedia Commons.
After Kenneth Koch’s poem One train may hide another.
captcha is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart. It can involve asking the user to identify distorted text, listen to audio files or identify tessellated images of zebras crossing or zebra crossings or other randomness.