The original recaptcha was used to help clear up text from book digitization projects where OCR couldn't understand the data. The appeal of this was that these works were in the public domain, and thus proper digitization of these works is a societal-wide benefit.

Since Google purchased it, they've been using it to:

1.) Clean street view data for a proprietary product (Google maps)

2.) Build training sets for unknown ML purposes

These are activities that Google could very much pay a group of people to do. Instead, through recaptcha, they are getting that work from the end user for no payment. A case could be made that it's not free for the owner of the site that deploy recaptcha (because they get value out of the service, and Google gets data/ML services). However, the actual end user who has to fill out the recaptcha does not benefit in any significant way. Since a recaptcha is an inconvenience to the end user, that user pays both with the time to fill it out, and the data gathered by Google.

TL;DR Some people do not like that Google benefits from a transaction where Google is not a party, and where otherwise, Google could generate the benefit using their own resources.

According to Wikipedia and the New York Times, reCaptcha was not developed for public domain works. Its pilot project was to digitize the NYT archives, archives which were not released to the public domain nor are fully available without being a subscriber: http://www.nytimes.com/2011/03/29/science/29recaptcha.html

I'm not a machine learning expert but I'm going to laugh at your suggestion that Google could "pay a group of people to do". In the above referenced NYT article from 2011, recaptcha's creator says several million words were being processed by recaptcha per day.

And again, have to disagree that the end user "does not benefit in any significant way". We would not be discussing this if Google hadn't learned from massive user data to iterate their captcha from distorted word mush to what it is today. Captcha was a serious drain of user energy and patience, that's why recaptcha was invented in the first place. And the worst captchas were tolerated because automated usage was a financial threat to websites that end users use.

It was provided a free service[0] (search free). I'm pretty sure that no one in this conversation is saying that the cost to run the service is free, and arguing such is a strawman.

was not developed for public domain works.

pilot project was to digitize the NYT archives

While the original "recaptcha.net" website is no longer available online (even via archive.org). There are plenty of sources still available that bely this claim. that will help convert printed text into computer-readable letters on behalf of the Internet Archive[0]. The team is involved in digitising old books and manuscripts supplied by a non-profit organisation called the Internet Archive[1]. "There's still about 100 million books to be digitised, which at the current rate will take us about 400 years to complete - Luis von Ahn, Carnegie Mellon"[1]. The sources are from 2007, when recaptcha was first introduced. There are more, but I picked the first two by going back to the beginning of the wikipedia entry for recaptcha and looking at the supplied sources.

This is before Google bought it in 2009. While I can't speak for anyone else, this is what I mean when I say "original" recaptcha.

laugh at your suggestion that Google could "pay a group of people to do".

They got a group of people to do it for free, which implies (barring salaries) that they could also get a group of people to do it for not-free. Thus the argument that people don't want to work for Google for free.

Google hadn't learned from massive user data

And when Google has met it's ML goals and decides it gets no further benefit from recaptcha? Remember, it's not a free-to-run service. They only continue it as long as they benefit. If recaptcha shuts down, it would have been nicer to have the fruits of that work available through something like the Internet Archive, than something like Google Books.

[0] - http://www.cmu.edu/news/archive/2007/May/may24_recaptcha.sht...

[1] - http://news.bbc.co.uk/2/hi/technology/7023627.stm

This isn't true. The end user benefits in a very obvious way by being able to use a site that hasn't been crippled or spammed by bots. It is very possible that many sites either would not exist or would be of much worse quality without a recaptcha-like service.

Everyone profits from recaptcha.

In other words, if Google's service didn't exist, you'd be experiencing less of the site, or no site at all if they chose to use a paywall that you refuse to pay for.

Anyway, I am not completely against it, as I said above depending on the situation I make use of it.

The value Google gets from the thing they want, and the value you get from the thing you want, aren't particularly comparable.

IMO, this is strictly better.

Google is using ReCaptcha as measure to get an unfair edge over competitors and make competing even more impossible.

You must not be living in the U.S. Even as strong as the FOIA and public records laws are, there's a huge amount of information and records that are exempted from free access:

http://www.rcfp.org/browse-media-law-resources/digital-journ...

Does a sweet pastry count as a cake? Is this stretch of water a river, a lake or the sea? Are those trees I see in the distance on this photo of a mountain? Does the front of a restaurant or a veterinary surgery count as a "storefront"? As a British English speaker I had to guess at that last one, and some of the others seem culturally dependent too.

Or, my personal nemesis, the ones which ask you to select the squares containing road signs, and there's always a couple of squares containing a 3-pixel strip of the very edge of the road sign, and you don't know whether you're supposed to count those or not.

Of course the site (and with it visitors) benefit in this exchange, so I agree with you that it is not entirely "free".