Putting someone's picture (that happens to be on the web, publicly available) in a post on a site, where you happen to have ads does not count as "using your image" for commercial purposes. Putting your image in an ad would.
My point is that you shouldn't be able to just claim having copyright over someone's work, and then profiting from it as your own. I shouldn't be able to take the HD version of Iron Man 3, and then sell it to my local cinema. That's as far as copyright should go.