Strange Photo at the Trier Cathedral Courtyard

This are some of the photos I took at the courtyard of the Trier Cathedral in Germany. Photo#1 was the first photo and you can see that it is clear. The next photo I shot was of the hallway in front of my husband and daughter. You'll notice that there are some spots on the photo, just like photos 3 and 4. Photo#5 was taken by my husband and it was on the opposite side. You can see a big spot on top of my head. I know that these are not some kind of dirt or dust since the photos before, after and in-between these photos are all free of spots. I also have some photos I took at the Trevi Fountain and St. Peter's Basilica in Rome that has spots on it. I noticed these after I downloaded all the photos in my notebook. What do you think? Strange eh?