If you believe in themes, pick Anniversary photo frames based on a theme. Themed frames are quite popular and available in aplenty in the market. Take your pick based on the tastes of the couple, and surprise them with it.
Before gifting them with Anniversary photo frames, inquire if the couple have wallpaper on the walls of their home. This is because; the frame should always be in contrast with the wallpaper in terms of color, texture and design. Contrasted frames actually complement the walls because of the great appeal they create as contrast to the wallpaper.