Removing References

Section 4a of the license states, in part,

If You create a Collective Work, upon notice from any Licensor You must,
to the extent practicable, remove from the Collective Work any reference
to such Licensor or the Original Author, as requested. If You create a
Derivative Work, upon notice from any Licensor You must, to the extent
practicable, remove from the Derivative Work any reference to such
Licensor or the Original Author, as requested.

Per DFSG 3, any licensor should be allowed to make and distribute modified
versions of a work. The above clause allows a licensor to prohibit modified
versions that mention them or reference them.

For example, an author who made a novel available under an Attribution 2.0
license could give notice to disallow an annotated version that mentions the
author by name or simply as "the author".

A more specific example for Debian would be a programmer who creates
documentation licensed under Attribution 2.0. He could require that
references in derived versions to design or implementation decisions he made
for the program be removed.

In addition, Section 4b of the license requires that the author’s name,
copyright notices, and some other information be included in derivative
works, "if supplied".

It’s unclear whether the creator of a derivative work can comply with the
requirement to remove references and also comply with the requirement to
give attribution. It’s not specified that a licensee who has been asked to
remove references to the licensor has the requirements of attribution
waived.

If a request to remove references can make it impossible for licensees to
comply with section 4b, and thus makes it impossible for them make
derivative works (DFSG 3) or collective works (DFSG 1), the work is not free.

Any Other Comparable Authorship Credit

Section 4b describes the requirements for crediting the Licensor for his or
her work. It states, in part:

Such credit may be implemented in any reasonable manner; provided,
however, that in the case of a Derivative Work or Collective Work, at a
minimum such credit will appear where any other comparable authorship
credit appears and in a manner at least as prominent as such other
comparable authorship credit.

There are several ambiguous or vague terms in this clause.

"any other"

This can mean "some other" or "all other". The first would mean that
authorship must be credited somewhere, and particularly where other
credit goes. The second would mean that authorship must be credited
everywhere that authors are credited.

"comparable authorship credit"

This could mean either "credit for comparable authorship" or "comparable
credit for authorship". The first interpretation would allow crediting
an author with all other authors who have made similar contributions.
The second would require crediting the author where any author is
credited, even if the level of contribution is not comparable.

A licensee cannot exercise the rights granted in the license if they can’t
meet these requirements. For this reason, the most pessimistic
interpretation of the requirements must be used. This would require
attribution for the licensor everywhere that authorship credit is given,
even if that credit is inaccurate, and even if the licensor’s contribution
is not comparable to others. Some examples:

• If a work is a collection of essays by different authors, with authorship
  credit given in the chapter titles, the Licensor’s name would have to be
  listed for each chapter title, even if they did not contribute to it.
• For an encyclopedia with a large number of authors, all authors would be
  listed at every point of authorship notice: on the spine, on the front and
  back covers, on the title page.
• If Alice writes her autobiography, and includes lyrics from Bob’s song in
  one chapter, she must give him credit for the entire work: "The
  Autobiography of Alice, by Alice and Bob", or even The Autobiography of
  Alice and Bob.

Requiring inaccurate or excessive authorship credits is an unreasonable
restriction on distribution (DFSG 1) and making modified versions (DFSG 3).

Anti-DRM clause

Section 4a says, in part,

You may not distribute, publicly display, publicly perform, or
publicly digitally perform the Work with any technological
measures that control access or use of the Work in a manner
inconsistent with the terms of this License Agreement.

It’s not clear which if any "technological measures" would be consistent
with the terms of the license. Because of this vagueness, we have to take a
worst-case view and consider that there are no such measures that are
allowed.

If this is the case, private distribution of the work would seem to be
forbidden. Along with obvious technological measures that control access,
such as a firewall on a LAN or a virtual private network (VPN), distributing
using encryption (such as Secure Sockets Layer (SSL)) would appear to be
prohibited.

DFSG 1 requires that works be freely redistributable, both publicly and
privately. Disallowing private distribution appears to be incompatible with
that goal.

Trademark Restrictions

The only version of the license available from Creative Commons is a Web
page that includes the following text:

Except for the limited purpose of indicating to the public that the Work
is licensed under the CCPL, neither party will use the trademark
"Creative Commons" or any related trademark or logo of Creative Commons
without the prior written consent of Creative Commons.

These restrictions make excessive demands on both licensor and licensee, and
abridge their fair use rights to the Creative Commons trademarks. This puts
an excessive burden on the licensee and effectively prevents redistribution
(DFSG 1) and modification (DFSG 3). In addition, it violates DFSG 9,
"License Must Not Contaminate Other Software", since it prohibits fair use
of the trademark even in works unrelated to the current one.

Note that the HTML source code for the Web page includes a comment that the
trademark restrictions are "NOT A PART OF THE LICENSE". In a graphical Web
browser, the text for the trademark restrictions are visually distinct from
the license text. Creative Commons representatives have stated that the
trademark restrictions are not part of the license. Finally, the same block
of text states, "Creative Commons is not a party to this License, [...]".

However, debian-legal feels that the visual distinctions are not
sufficiently clear to indicate that the trademark restrictions are not part
of the license, and some instances of the license found in the wild include
the trademark restrictions. The relation of the trademark restrictions to
the license proper is sufficiently ambiguous to make it difficult for
licensees to comply.