Possibly the only difference in quality is in duration. Sunlight is a continuous light source while a camera strobe is a short duration burst. It could be the intensity of the light source, which could be higher or lower depending upon the capabilities of the camera and the flash units. Or it could be color of light. That would be measured in color temperature on the kelvin scale. On earth, camera flash units are calibrated for about 5600 degrees kelvin, which approximates the color temp of the sun. Lower numbers indicate the light is more to the red end of the spectrum and higher ones more blue. I'm not sure what the color temperature of sunlight on Mars is, I would assume a lower [reddish] color, but unless this was factored into filters on the camera flash units, it is possible that they are firing at a higher [bluer] color than ambient light on the planet. It depends a lot on what frame of reference the designers of the probes were using...Earth local or Mars local.
Does this help?
Captain Zot