Regarding his action, Lenssen says:
In other words, Google imposes restrictions on these books which the public domain does not impose*. I’m no lawyer, and maybe Google can print whatever guidelines they want onto those books. . . and being no lawyer, most people won’t know if the guidelines are a polite request, or legally enforceable terms**. But as a proof of concept—the concept of the public domain—I’ve now ‘set free’ 100 books I downloaded from Google Book Search by republishing them on my public domain books site, Authorama. I’m not doing this out of disrespect for the Google Books program (which I think is cool, and I’ll credit Google on Authorama) but out of respect for the public domain (which I think is even cooler).
Since Lenssen has retained Google’s usage guidelines in the e-books, it’s unclear how they have been "set free," in spite of the following statement on Authorama’s Books from Google Book Search page:
The following books were downloaded from Google Book Search and are made available here as public domain. You can download, republish, mix and mash these books, for private or public, commercial or non-commercial use.
Leaving aside the above statement, Lenssen’s action appears to violate the following Google usage guideline, where Google asks that users:
Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for personal, non-commercial purposes.
However, in the above guideline, Google uses the word "request," which suggests voluntary, rather than mandatory, compliance. Google also requests attribution and watermark retention.
Maintain attribution The Google ‘watermark’ you see on each file is essential for informing people about this project and helping them find additional materials through Google Book Search. Please do not remove it.
Note the use of the word "please."
It’s not clear how to determine if Google’s watermark remains in the Authorama files, but, given the retention of the usage guidelines, it likely does.
So, do Google’s public domain books really need to be "set free"? In its usage guidelines, Google appears to make compliance requests, not compliance requirements. Are such requests binding or not? If so, the language could be clearer. For example, here’s a possible rewording:
Make non-commercial use of the files Google Book Search is for individual use only, and its files can only be used for personal, non-commercial purposes. All other use is prohibited.