Since you purchased your CryptoKitty, also check out the First Sale Doctrine.
Since my first reply, I see other Steem writers posting images of CryotoKitties. If Steemit.com were receiving takedown notices from the CryptoKitty copyright holders, I feel we would have heard about that by now.
I am not an attorney, but if someone ever messes with you about posting an image of your Kitty, or other item that you have purchased, then feel free to contact me. I am rusty, but have a strong background in takedown notices, and the DMCA.