Doug can likely answer this better than me, but it is probably due to the enhancement algorithms in your camera's/phone's software. Colors and contrast are often boosted and that is going to dramatize variations in a coin's surface. Also, my camera focuses better than my eyes, so "in hand" most of my coins have marvelously pristine surfaces .
Sad but true. Coins are small and usually seen in poor light. We enlarge them 10-100x and shine bright lights on them bringing out everything we don't want to see. The internal JPG processing algorithms built into cameras (especially cheap ones) emphasize contrast and artificial edge sharpness since people like their pictures snappy and clear even when the light is dull and boring. People don't want pictures that make them look ordinary when they can have extra added pizzazz. Truth is not the first consideration in photography.
To JWT, try using three lamps; left, right, and front. Works especially well with a plastic dome over the coins, then adjust your coin accordingly. I shot this a bit hot but will adjust the exposure in LightRoom or PhotoShop.
This shot with three lights....... Sorry for the un-ancient nature of the photog......... I can feel ancient 'sorts', mumbling in the background, that that green fellow 'slimmed' us again. It's a 'drive by' photoging.......somebody call the police.
