Do you code? How about you send me the source to your best known, commercial product, and then I'll reformat the source, call it a derivative work, and sell it. That's cool, right? Of course not.
I see this as being not that different.
Which really brings up the key to this, which is what is considered "derivative". Everyone has a different concept of it, I'm sure, and it's not cut and dried.
To me, simply taking a picture someone else took, and digitizing or pixellating it, is not something that I would consider "derivative". I liken it to sampling music to be used in a "derivative" work. In the vast majority of those cases, the samples have to pass through the proper licensing and be released for use before they are resold.
And while the guy might not have created the content of the picture, he spent the time and effort to actually go and take the picture. Doesn't matter if he spent a month setting up the content and lighting to get the perfect shot, or sat on his cel-phone camera and it took a great picture as a result of blind luck, it's his picture.
If he wants to sell that picture for profit, and has cleared the rights of the content of it, that is his prerogative.
I think that the pixellated image would require something similar to a mechanical license that you find in the music industry, where someone creates the song, but then gives the rights for another band to record and sell their version of it.