How to retrieve photos from itunes back up?

Hi! Good day! I just restored my iphone (SE) to its factory setting via itunes and of course I had it backed up there. After I've restored my back up, I noticed in my gallery, a 6 months worth of photo and videos is blanked out (all white). When I try to edit one white photo, a prompt message pops out "Cannot Load Photo There was an error loading this photo." I tried to restore my previous back up for the second time but no luck, I still got the same results. How can a retrieve those files? Some of those files are my notes. Thank you in advance for the help, will be much appreciated.