Object in image 1 and 4
There is a distinct dot which appears in the first and last image of this set but not in the other two. In the first it's located just above and to the right of centre, and in the last it's in the lower left corner.
I marked it as an artefact in two images but I'm not sure if that's the right thing to do. Any suggestions on how to treat in the future or what might be the origin?