While pictures like that look impressive, they're not necessarily significant. Humans only occupy some 10% of the land on earth, which just isn't much.
Humans can pollute a lot more land/water than they occupy with their physical bodies.
I bet that Ganges River is not as clean now as let's say 10 000 years ago.
Yeah, but India is one of the most populated places on earth. Fix India and teach them sanitation and you've got a clean Ganges. Shitting in my toilet doesn't mean that yours is about to get dirty though. Just like an ant colony shitting in my backyard won't pollute that of my neighbour.
One big oil tanker crashing and leaking can cause a lot of damage even in less populated areas (e.g. Alaska 1989).