Wikipedia puts the total African giraffe population at 110,000-150,000: http://en.wikipedia.org/wiki/Giraffe. So there are more pictures of giraffes than actual giraffes.
As countries grow in wealth and life expectancy, the number of children per woman tends to drop off drastically.
How many drawings and human-shaped sculpture are there on those social sites? I doubt there's more than the 6.8 billion you quote from wikipedia.