1. A computer-implemented method for distinguishing a live actor from an automation, the method comprising steps of: receiving, from a user, a request to access a service; in response to the request, audibly presenting to the user a minority set of objects of size N and a majority set of objects of size greater than N, wherein each of the objects appearing in the minority and majority sets is an image or a text that has an alt tag allowing the image or text to be audibly identified, and wherein N is a natural number and the majority set includes objects sharing at least one common attribute expected to be apparent to a human observer and to be absent among objects in the minority set; requesting the user to identify, based on the audible presentation of objects in the minority set and majority set, at least one object, from among the objects in the minority or majority set, that satisfies a predetermined criterion related to the at least one common attribute; receiving, from the user, an indication of a selection of at least one object; determining whether the user-selected object satisfies the predetermined criterion; and determining that the user is a human upon determining that the user-selected object satisfies the predetermined criterion related to the at least one common attribute.