The pokestops you see without images are usually imports that Niantic (now Scopely Explore) added to the database to make games playable in places where there wasn’t anything. These imports often did not meet the criteria that a submitted Wayspot would have to. If you give me the location of one, I can check the map to see if this is the case.
Many Wayspots that are not eligible to become pokestops were added to create a Power Spot data base. Clarifications on Pokémon Go Power Spots
Another reason you may see a Wayspot without a photo is if the photo has been removed.