I tried the File Manager, Gallery, and Photos. They all loaded the MP4s but the photos weren't listed. I copied all the folders to an SD Card, where all the folders loaded, photos and videos. I was able to view the photos in Gallery, Photo, and the File Manager. The USB still only listed the MP4 folders and files.
I opened the files on my PC to make sure they were there. My sister has the same problem. Her wedding photos were given to her on a flash drive. Th photos are JPEG.