Should one photograph the equipment as proof of ownership?
Maybe put the photos in a safety deposit box?
In my safety deposit box I have physical photos of various possessions as well as USB sticks with photos. However, I believe USB stick data will last only about 10 years unless rewritten.
Safety deposit box? Sooo stone age!
Photograph your expensive gear. Make a spread sheet (or just a word doc) with serial numbers, model numbers, replacement value, etc. Put thumbnail sized images in the file with the file names of full sized photos. Upload it all to a free "cloud" account - dropbox gives you a free GB, I think google gives you 10 or 20 gigs. As you get new gear, it's easy to add that to the list.
My agent just laughed when I described my gear - dozens of packs and heads, HMI lights, hot lights, cinema stands and grip, film, digital and video cameras, a crazy amount of audio gear... he said I'd need a business rider and documentation of all the stuff, but as i recall, the price he quoted was reasonable and covered me when traveling, too (I do a lot of location work with digital, and usually bring an RB rig or an isolette if I drive far). Haul all that crap into motels, too.
So for me it makes sense - you really have to do the math and see with premium and deductible is worth the expense. You're often better off to get a premium quote, and open a savings account and religiously put aside that amount each month. Basically be your own insurance company. 15 years down the road without a "claim", and you could have a nice little sum.
The only things I would have claimed in 20 years: a theft of a light meter and Schneider loupe, probably by a delivery guy, $400? And a dropped Sigma lens. Both lower than deductible. But a fire or serious theft could wipe me out, so I'm working up my inventory documentation.