Can I Use Image If There is No Copyright?

Dear Rich: My question is a question about copyright as well as a question regarding your blog. I'd like to use an image from your blog (from this entry) but as you didn't specify who was the author, I don't know if it is copyright-free. So my question is: do I have the right to use an image if there seems to be no copyright? As regular readers of our blog know, any picture first published after February, 1989, is protected under copyright regardless of whether copyright notice or attribution is included. As a general rule you should presume a photo is protected unless the photo indicates otherwise.
So who owns the image? We created this image which is a derivative work. We're heavy users of iStock and we're pretty sure the photo of the books was licensed from that site. We added the mesh background and balloon captions (which is probably a violation of the iStock license agreement - please let sleeping dogs ... etc.). If we'd created the whole thing, we'd gladly permit you to use the image with attribution but since we don't own rights to the underlying photo, we can't offer that. However feel free to apply our captions over your own bookshelf.