In discussing licensing options for open education items, I suggest that the CC BY license is in many ways the most open license. While share alike sounds like a great option, because it prompts sharing down the road, it is sometimes overly restrictive. It’s not always easy to envision how this might the case, so here is an example.
I am working with a school district to create a series of movies that highlight vocabulary and essential questions in their social studies curriculum. The essential questions come from their textbook, and the publisher has given permission to include these in the movies. Because this material is copyrighted, however, we cannot “share” the movies we are creating beyond this district (or others to whom the publisher has extended permission). As such, we can’t include any share alike images. This eliminates a lot of great material.