It's probably a no in your case.
It's a really tricky one and nobody knows the answer.
The general idea is:
You're allowed to come 'on business' but you're not allowed 'to work'.
This would have to be the most bent rule on the planet, though.
Then there are people who try to push the envelope
Work as freelancer while tourist in US for an already existing US client?
The tricky thing in your case is ...
The damned cameras!
About 18 billion programmers waltz in to the US every day ("I'm just going for a meeting!") and then work their asses off. Who doesn't have a laptop? It does not look "work-related".
But. In your case you'll show up with photo gear; your profession is just different. Due to the equipment to begin with.
Say you were (honest to God) going only to have a production meeting about a project. That is 100% bona fide. You would just be "doing business". But if you're scouting? Tricky. Actually shooting? You're then like the tidal wave of programers who fly to the states ("just a meeting!") and then in reality work their asses off.
As a factual matter I can think of 5? folks known to me who've done this over the years and it's a total non-issue.
But in your case you're doing it repetitively - pretty much every month.
I really just don't know how that plays out.
My guess is probably "No" unfortunately.
Unfortunately this is a couple yrs old: