Image used without approval

Have you ever had one of your images used without your permission? I have and found out about it when my husband did a Google search using my name and came across my "Blue Man Walking" image on a cover of an E-book. First off i was pleased because the image is credited but then i couldn't figure out if i had submitted the image or gave permission to a friend? So i contacted the editor at BlazeVox and asked how my image got to be on the cover of this particular publication. He wrote back immediately and said that the author got my approval and gave me the author's email address. Again, i asked the author how he came across my image etc... and the author wrote that he was "aimlessly messing around on the web" and liked the image because it came close to the image he had in this mind of what the character looked like. He apologized for not getting permission.
Hmmmm, have i just been a victim of the work of unscrupulous people who target unknown artists on the web to find images for their own profitable uses (the author has had almost 6500 downloads), thinking that it won't be found out? What can i do? Oh well, update the old resume, i guess.