It it reCAPTCHA - it isn't as smart as you think.
Two words are presented to you;
One is unknown by the "computer"
One is generated by the "computer"
You can easily tell which one is generated. This is the
check-word. For example:
'the' is generated by the computer
'plerpit' is unknown by the computer.
Just write the check-word (the) and anything you want at the barely readable one, and you will go through. What it does is basically add your answer to the unknown word to a database, and
later on look for similar matches. Once enough are found, it is marked as a known word and from what I know Google Books or w/e it's called is using this, a pretty neat function.