Derivative Credits

Hi,

I'm working on a book about state symbols. Suppose I find public domain images of California's state flower and tree and make my own picture of the state flag. I modify the first two pictures and combine all three into a single picture that I can now claim as my own.

Now suppose I purchase a picture of California's tree from Adobe. I modify it and add it to my bigger picture.

What would be the proper way to legally describe the resulting picture? Can I say "Copyright David Blomstrom," or would I have to say "Copyright David Blomstrom...except for the state tree, which I purchased from Adobe"? Or should I describe the work as a "Derivative, copyright David Blomstrom," or something like that?

Thak you.