Dead Pixels or dust on the lens, you might as well get busy doing the research.
Do some careful easy research with free tools. The NASA/JPL data gives you position, time and other information for each exposure. With that there are
several astronomy programs, some free, that you can observe the star positions from Mars on time and date. Find your programs here.
Free-Shareware-Buy Astronomy Software
The simplest you might have. Google Earth in Mars mode. Although Google Earth stellar information and positions of Phobos/Demos might not render, you
can see if the thin atmosphere is letting a stars/planets light through in a long exposure or otherwise opportune moment. If Venus, Earth or Jupiter
is up, it might just be visible at a martian dusk.
I have software I can see all the stars and moons, major planets and even galaxies and nebula from anywhere in the solar system. Starry Night is a
good paid astronomical software if you have the $.
Eliminate the common causes first, then ask others, then when all is exhausted it becomes an UFO or unknown. But unless it is showing unusual or
otherwise anomalous movement, structure or emission of lights, look for the common possibilities first.
This looks like Dead Pixels
or I hope, dust, but dust would not be so sharp as if on the lens
would not be in the focal range of the camera. In fact, if you have dust on your lens you will not see it, nor does it degridate the image very much
at all. See Why
When my laptop gets a dead pixel it is a vertical line going across my whole screen, but on other CCD and LED arrays it can just be a spot or cluster.
My Digital SLR has dust on the actual CCD, and that will show as distinctive spots. Check for that stuff like you did here, just noting the position
in the frame, and looking for it in other frames. If not anywhere else it might be a transitory dust spec or something else.
Keep looking, because if there are UFO's here, it is likely they are on Mars too. I fully expect to find life on Mars, and throughout the known
galaxy and universe. Soon we may have direct evidence. But we need to be sober and critical of everything so as not to disappoint and loose others who
depend on us to tell them what is real.
Crying wolf when there are no wolves too many times and eventually no one looks, even when we have evidence to the effect.
Do the work and don't cry wolf so easily. This is important!