My personal, concrete experience of these matters is that authors willing to use my images (which are licenced under CC-BY-SA) feel the need to write to me to acertain the autorisation. One even mentionned that he would not have written if I had licenced my images under CC-By (which I do not wish to).
<br><br>So arguably, the ambiguity on this matter is harming the diffusion of our work. Because for one person who writes to me, several maybe decide that they won&#39;t bother, and probably more misunderstand the licence and assume that using Free images has effect on the entirety of their work.
<br><br>-- Rama<br><br>(PS: I also find my images here and there without attribution or with the attribution but without a licence, but that&#39;s another matter :p)<br>