These side-by-side images were taken by the Pan Camera (Pancam) on NASA's Opportunity rover. They're actually the same image; the left version is how the image originally came down, due to data dropouts. The right shows the same image after processing all the data. The image is from the 4,493rd Martian day, or sol, of the mission. https://photojournal.jpl.nasa.gov/catalog/PIA23248