Technically the forum rules state that the image is now "public domain":
"General Items:"
"* Posting on BYC makes the comment, images, ideas "public domain". If you decide to leave the forum BYC will not be required to remove your posts."
and if he asked anyone running BackYardChickens if he could use it, then he can:
"You also agree that posting material to our forum and website implicitly grants BackYardChickens a non-exclusive, worldwide, royalty-free, perpetual, non-revocable license to use and change said material for the purposes of running BackYardChickens."
https://www.backyardchickens.com/forum/misc.php?action=rules
It would be nice if he had asked, if he indeed knew how to contact you. Someone might have copied it and sent it out in an e-mail because they thought it was cute and so did he so he used it, having no way to know it's source and figuring it was already public domain. Darn it, the internet sure can complicate things, as I see your points and find them rather agreeable wildsky.
But, after being contacted and being asked to quit using the picture and then using them anyway.
that's just not right...