The Tagxedo FAQ states:
Q: What is the licensing requirement for using images created or derived from Tagxedo?
A: The images created by Tagxedo, and their derivatives, are licensed under a Creative Commons Attribution-Noncommercial-ShareAlike License 3.0, and must be attributed to http://www.tagxedo.com. The images created by Tagxedo and their derivatives are free for personal use, including usage on personal blogs, non-profit organizations, and non-profit education institutions, subject to the Creative Commons Attribution-Noncommercial-ShareAlike License. For more information on licensing please contact firstname.lastname@example.org
If I created the image and the fonts' authors claim no rights over my use of their font, should the image not be mine? Is this permissible under United States copyright law?