Can an amateur-built aircraft ever be used for commercial activities?
According to the Experimental Aircraft Association (EAA), aircraft with Experimental/Amateur-Built airworthiness certificates cannot be used for commercial purposes. However, I cannot find an FAA reg that specifically says that. (Anybody else know of a reg that says that?)

There are other grey areas as well. For example, what if your insurance is requiring dual instruction in the type before they will issue you a policy? The CFI would be using your aircraft for commercial purposes, even if you can legally claim you're the Pilot-in-Command. 

However, the FAA talks about what things you cannot do without a commercial pilot license -- fly passengers or cargo for hire. My suggestion is that if you want to use your amateur-built aircraft for commercial photography, call your local FSDO and ask about that. Be nice to them and you'll be impressed how nice they can be to you.