I think it's a distortion as there's a lot of banding around it.
However that lump of coral in the foreground is really interesting and just like the one I've got on my hall console. Oh forgot...Mars.

Originally posted by expat2368
I found the original image on the NASA website. It is interesting that the original image has a lot more contrast and detail than the one the link points to. The "original" image they have available for us peons to see is a 223kb image. The one the link points to which is low contrast and shows exactly the same area is 271kb.
I would guess there is another master image that both were taken from. I would like to see the original high resolution image but I do not see a way to find them. It is also interesting that a previous image of almost exactly the same subject matter does not show the spot on the horizon.
Here are the two images that are not so washed out both of the same view:
Original image: (with spot)
marsrovers.nasa.gov...
Next image: (no spot)
marsrovers.nasa.gov...
