You could access Photos through the VR Browser (http://photos.google.com) or if you install the sideloader app for Gear VR (premium), then you can load Chrome VR and do the same.
I think there's also a Google Photos app for Daydream, but the S7 isn't Daydream-compatible (the S8, I believe, was supposed to be, but I don't think support has rolled out there either). You MIGHT be able to sideload with the above app, maybe? If not, using the browser is your best bet.