From: Markus <markus@...>
Date: 2004-10-27T00:09:23+09:00
Subject: Re: Garden Spam

On Tue, 2004-10-26 at 01:33, Brian Candler wrote:
> >      Think creatively.  You could fairly easily come up with a text
> > based captcha system that was screen reader friendly and had no external
> > dependencies.  For example test riddles / story problems that would be
> > dirt simple for a human but next to impossible for a program "in the
> > general case" could be rather easily generated in pure ruby.
> > 
> >     For example:
> > 
> >           Three things that go "quack" landed in a circular pond
> >           that was 10 meters across.  They found fourteen early shoes 
> >           and each of them ate as many as he wanted.  How many shoes 
> >           were left?
> > 
> > Most humans could get this on their first try
> 
> I disagree; I'd be surprised if more than 10% of the general population
> could get past that barrier (although maybe if you gave them two or three
> tries you'd get more).

     *smile*  Less than that, because the majority of the general
population does not know english.  I someone else noted, this was a
contrived example (and, I gather, not a very good one).  But note also
that I suggested having a quiz/contest to come up with better ideas--the
important point here being the general structure, not the particulars.

> Perhaps that duck example is not typical of what you were proposing, but in
> any case I find it highly ambiguous. Are we supposed to assume that ducks
> don't eat shoes? (=> Answer 14). Or to assume that all the shoes would be
> eaten? (=> Answer 0). Since we are clearly in a nonsense world here, with
> such things as "early shoes" which don't exist in the real world, we can
> apply whatever rules we like to come up with an answer.

     I tried to cram all of the proposed mechanisms into one example
(all except the spelling errors, which I hadn't thought of yet); I see
now that this was a very bad way to present them.  Imagine instead of my
duck problem a whole collection of questions that require different
sorts of answers but look structurally similar to some of the other
questions in the collection.  In other words:

      * If I have seven pairs of shoes how many shoes do I have?

      * What goes "quack"?

      * In "The tired man gave algebraic his wife a kiss" what word
        doesn't belong?

      * In "Bananas are generally yellow or greed?" what word is
        misspelled?

      * If you could have all the shoes you wanted, how many would you
        eat?

      * ...and so forth


     If these questions were "randomly" generated be a heterogeneous
collection of simple plug-ins, it would be easy for us and hard for
them.  

> Or, given that there were 14 shoes, perhaps 7 were right and 7 were left.
> (Argh!!)

     Yes, putting all the obfuscation techniques in one example was
definitely dumb on my part.  Sorry.

    -- Markus