In no event shall any speck of dust as the majority suggested, as in the second picture it is present as well, but a little distant and changing positions relative to the planet.
Judging by the time stamp on the picture, the difference between the images is 17 seconds, but during that short time, so the project has managed to move far enough. This only proves that this triangle was moving at a fairly high speed. That is why, the hypothesis of space debris was immediately ruled out.
Incidentally speaking, these pictures were taken with a hand camera, and it is likely that the astronaut who made these amazing shots could personally observe this unknown object, which then was in Earth orbit.