I think it’s on the lens (probably in software) to identify the top of the image that is actually Mars. The dark part at the top of the image that looks like dark sky is actually part of the rover, everything below that is Mars.
Think of it like a camera under a car, the dark band at the top is the bottom of the car.
It's just a mouse cursor, this image is from a feed of the software they used to receive images and the cursor was on top when the screenshot of the stream was taken.
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u/[deleted] Feb 18 '21
What is that cross looking object on the horizon?