A native speaker might say we took a photo to remember (or mark) the occasion. I would never use the term commemorative photo or souvenir photo. But if someone said either one, I would understand what they were saying.
When I think of a souvenir photo I think of the photos that are taken of someone when they are on a cruise ship or on a roller coaster or on a zip-line. You look at the photo taken by a stationary camera or a photographer and buy it from the business or from the photographer if you like it. They are usually expensive 😀