Happy Anniversary Sharon!
I love the idea of a special photo to commemorate your special day. There are Disney PhotoPass photographers stationed at several points in the Magic Kingdom. Typically you'll find several stationed on Main Street during the first hour or so that the park is open. Later in the day, there are usually PhotoPass photographers on the bridge between the main hub and Tomorrowland arranged to get great shots with the castle in the background. They'll be a happy to take shots with your camera or theirs. If you explain that it's your anniversary, they'll likely be willing to spend a few extra minutes with you getting just the right shot.
If you'd like something more planned, I suggest that you arrange a portrait session with the
Disney Fine Art Photography Department. I simply can't say enough wonderful things about this group. You can choose locations at many of the resorts or at Epcot to have a full dedicated photo shoot. I did this with my family last Christmas and THRILLED with the results. I hadn't had formal portraits taken since my wedding 20 years prior, so these were a real treat to be cherished. There are long and short versions of the photo shoot available at different price points.
There are sample photos on the Disney website at the link above, but if you'd like to see some of the Moms Panelists' portraits, head on over to the independent website blog.touringplans.com. Search there for an article called "Disney Fine Art Portrait Sessions," where you'll see many of the Moms real photos.
Good luck with your planning. Please let us know what else we can to do make your anniversary even more magical.