Maybe I'm missing something here but...what problem exactly does this solve? I understand the underlying concept, but I don't see how a picture takes care of the issue.
Ok, you have a picture of it as a "pistol". So? All that shows is that at sometime or the other it was in a pistol configuration. It doesn't prove that it was a pistol first. Shoot, that thing could have been an SBR rifle for 6 months, or 6 minutes, prior to this picture being taken. If no one in an official position (that matters) saw it and took note of the fact that it was either a pistol or rifle, and when, I don't see what good a picture does. Truthfully, I don't see what good a picture does period when it comes to proving anything.
How can you legally argue to the BATF that "this particular firearm was built as a pistol first, so I can switch back and forth at my will so long as I never fall under NFA rules"?
It seems to me that the only way to be legally covered was if you purchased it as a pistol and it was registered "somewhere" as such, then you could convert it to a rifle and back AND be able to verifiably cover your butt.
I could build one of the lowers I have right now as your standard vanilla flavored AR, play around with it for YEARS then covert it to a pistol which legally I'm not supposed to do and play around with it for years again, and then switch back. How is anyone going to prove it?