I find it very amusing actually, being both a pilot and photographer at the same time.
Truth is, there's a ton of people out there who know a s**tload about aviation and the aircraft that come to their airports. They can probably tell you the previous five owners / operators from the top of their heads.
If you have ever been to LSZS you'll certainly be familiar with dozens of them around the perimeter fence and even on the apron (the airport is very cooperative there, having guides for them and making them take briefings online, similar to the one crew have to do).
Even though I am crew I still like to occasionally wander around the airport in my free time and snap some photos when the light is nice or the aircraft are somehow rare.
I don't get the "logging registrations" thing really, I just like combining two passions - aviation and photography. I also do commercial work for various business aviation operators, simply because a photographer who has a passion for aviation will certainly supply better material than one who doesn't care much.
That being said, if you don't like a photograph of your jet / yourself online, a short email usually makes the photographer remove it.
