I am an attorney (and as far as I can tell, the author is not one, so take his "analysis" with a pillar of salt). This is not legal advice though.
With respect to the following paragraph:
"So, if you snap an awesome photograph, upload it to your blog, and someone pins it, that person is either (1) claiming exclusive ownership of it; or (2) giving Pinterest your consent to reproduce it (and you just thought you were being flattered)."
Actually, no. You can't transfer a right you don't have. All rights to a work are vested in the author of a protected work; only the author can consent to any of the activities protected by copyright.
It's just like selling a house you don't own. First, you're committing fraud if you falsely represent that you have the right to sell it; and second, the actual owner isn't bound by anything you have done (the deed doesn't go to the putative buyer).
With respect to the following paragraph:
"So, if you snap an awesome photograph, upload it to your blog, and someone pins it, that person is either (1) claiming exclusive ownership of it; or (2) giving Pinterest your consent to reproduce it (and you just thought you were being flattered)."
Actually, no. You can't transfer a right you don't have. All rights to a work are vested in the author of a protected work; only the author can consent to any of the activities protected by copyright.
It's just like selling a house you don't own. First, you're committing fraud if you falsely represent that you have the right to sell it; and second, the actual owner isn't bound by anything you have done (the deed doesn't go to the putative buyer).