Welcome to the Apple Support Communities and thanks for asking your question about restoring your iPhone 7 from an iTunes backup and having all your photos show up as blank. I love having my photo library on my iPhone and it's my pleasure to help you out.
I'd like you to first go to iCloud.com and see if your photos are showing up there as complete photos and videos. If so, that's great, we'll be able to turn on iCloud photo library on your iPhone and the photos should repopulate.
Settings > Photos > iCloud Photo Library (switch on). If your photo library is larger than your iPhone, then also select Optimize iPhone Storage.
If you don't see the photos showing up on your iCloud account, then let's try to restore your iPhone from iTunes one more time and see if your photos come back this time.
Best wishes.