With the caveat that it's entirely plausible that I don't know what the heck I'm talking about...
I believe that the tax write-off for donating your services can only be equivalent to the true cost of tangible goods that you provide, and even then, if you're already writing them off as a business expense, you can't write them off again as a donation.
So while you may charge everyone else $1,000 an hour just to shoot, you can't write that off.
And while you may get $100 for an 8x10 from clients, you can only write off your printing cost when donating to a charity.
This is how it has always been explained to me, specifically when I donate photo shoots + print packages for charity auctions. I can say it has a value of $xxx, but there's no write-off to be had.
See this post at PhotoAttorney.com for related reading:
Deductions for Donating Photography to Charities.
As always,
ask a CPA.