I would change "human" to "biological entity"...we should not exclude extraterrestrials from the target audience...this is at the risk of offending non-biologic

I would change "human" to "biological entity"...we should not exclude extraterrestrials from the target audience...this is at the risk of offending non-biological (and probably also extra-terrestrial) entities, but they would presumably render all captchas obsolete anyway.