These silhouettes are in the public domain.  That means you can do whatever you want with them: modify, share, sell-- anything.

Most of them came from digitized texts found at www.archive.org

Some of the animals came from this Wikimedia Commons section:

http://commons.wikimedia.org/wiki/Category:PD-ScottForesman

If you would like to mention me and my blog when you use these that would be cool, but it isn't necessary.  If you are curious who the original artist was for any of these let me know and I'll do my best to track that down.  Thanks.

Telecanter 
http://recedingrules.blogspot.com/