it is when you have a picture of 5 - 7 generated letters (and/or numbers)
Hhhhm. I actually beg to differ. (Not that it's that important), You may be right that the number/letter thing is being called a Turing test, but it isn't what is commonly known as the Turing Test.
I always thought of the Turing test as being the one where you have to sit at one computer and either a person or another computer at the other, and the aim is to guess whether it's a person or a computer. (No programs have done it yet though...).
That's much more like the actual definition.
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The Turing Test (as I understand it) was first introduced by Alan M. Turing (1912 to 1954) in an article written in 1950 called "Computing Machinery and Intelligence". What we now have come to call "The Turing Test" was referred to in the article as "the imitation game"
It started with the following sentence.
I propose to consider the question "Can machines think?" This should begin with definitions of the meaning of the terms "machine" and "think."
In short, the Turing Test is meant to determine if a computer program has intelligence. In Mr. Turing's own words, the original imitation game can be described as below.
The new form of the problem can be described in terms of a game which we call the "imitation game." It is played with three people, a man (A), a woman (B), and an interrogator (C) who may be of either sex. The interrogator stays in a room apart from the other two. The object of the game for the interrogator is to determine which of the other two is the man and which is the woman. He knows them by labels X and Y, and at the end of the game he says either "X is A and Y is B" or "X is B and Y is A." The interrogator is allowed to put questions to A and B.
The modern understanding of the Turing Test is as follows.
The interrogator is connected to one person and one machine via a terminal, therefore can't see her counterparts. Her task is to find out which of the two candidates is the machine, and which is the human only by asking them questions. If the machine can "fool" the interrogator, it is intelligent.
I should add that the Turing Test has had much criticism and has been the topic of many discussions in AI, philosophy and cognitive science since Alan Turing first wrote the article. There have also been some fascinating books (fact and fiction) written on the subject.
For reference, the original article for Computing Machinery and Intelligence can be found by following the link.