Mac storage basics · Photos, music and video
Why do imported photos come with short .MOV files?
Short answer: They're the video halves of Live Photos, imported as a still plus a short .MOV with the same name. Delete the .MOV files if you only want stills.
Those are the video parts of Live Photos. When you import photos as files (for example with Image Capture), each Live Photo arrives as a still image plus a short .MOV clip with the same name.
If you only want stills, you can delete the .MOV files — the photo remains, but it's no longer a Live Photo.