The problem with his "hook" is that the doctrine has relevance when a copyrighted work is involved, but he provided no information that copyright law was actually in play.
I imagine he didn't feel the need because the Techdirt audience is generally at least somewhat familiar with copyright issues, enough to understand that copyright in the US is automatic, and thus the photo is copyrighted. If he took the time to fully explain every single detail of every issue he writes about it would be a boring blog.
A necessary predicate for any discussion of fair use regarding a specific work is that the work must be secured by copyright, which to this point has been assumed, but not shown.
The only way it might not be copyrighted is if there is no person who took the photo (a la the monkey selfie). There seems no reason to think that could be the case since it was a mother showing her daughter the dress she'd bought. Clearly she took the photo of the dress on purpose, so she holds the copyright on it*.
* even if it were a work for hire, which is an absolutely ridiculous suggestion, somebody would hold the copyright, even if it isn't the photographer
Fair use isn't required nor is it part of the plan, the image was released with full intention of it being copied, modified and shared, more like a creative commons license.
Did the original post contain a notice that it was licensed under CC or similar? If not, then it was copyrighted with all rights reserved (because that is automatically what happens in the US). In that case, without fair use, copying and distributing it would be copyright infringement, regardless of what is going on in the copyright holder's head. That is Mike's point (as I understand it anyway).