Might want to look at your Manual then. Sounds like the camera is doing what it was designed to do. Take snapshots of Plates and give that data in picture format, Most times cameras are in a format that a video could be unusable and taking a picture of the plate for storage is expected.
Now looking at your picture above the answer is in the answer I see as well. I was about to look up the manual when I looked over your pictures again seeing I had to go up looking for camera name.. Anyway picture 1 top left under the type of recordings it says it will record Snapshots of the plates the way you have it setup..