There are two different sort of dot photos. Theres the EFF (Raw Full frame, from my link to pancam codes and tips), which are 1024 x 1024 but hugely lossy compression. Then there are a series of ESF images (Raw Sub-frame) only 63 x 63 but with good or no compression. I recall a similar series from Spirit.

Looking at the sequence of photos, what I think they are doing is:

1) take a high-quality shot of where you think the sun is. Encode only the central region at high-res.
2) take a couple of low-quality shots of the entire sun-pointing sky region, in case the nav is screwed. That way, at least on earth they can begin to debug the process if it went wrong. Encode at lo-res since all Earth needs to know is "is the sun in shot, and if so, is it off-centre?"
3) take a tracking series of shots of the sun, and encode the central portion to high quality, so mission control can check for wavering track or any other errors.

If (1) and (3) check out, the nav is good. If not, (2) helps diagnose the problems.

Still don't know what the second dot is, though. It could be a lens defect, or it could be something real. Must look at the equivalents for Spirit...