Dark spot in a photograph of Fort Lalatte in Plévenon

Summary

In May 2008, a photographer took two images of Fort Lalatte in Plévenon. Upon review, he discovered a dark spot in one of them that he had not noticed when shooting. The spot does not appear in the second photograph. With no direct observation or additional testimony, possible explanations range from a technical artefact to an object passing in front of the lens, but none can be verified. GEIPAN classification C.