This image has an unsolved mystery. There seems to be some sort of electrical phenomena happening above the high voltage transmission lines. The real mystery is that they are visible darker than background. It means what ever it is, it is not reflecting IR. If they were white they could be electrical discharge on film surface while spooling the film for developing. They are also visible in only that one frame. All other frames on the film does’t show anything like this.
If you have any clue about what is happening please contact me.