Answer
About 80 Gbit/s. In review, anything from 40 to 160 counts as right.
The worked estimate
50,000 × 200 KB = 10,000,000 KB = 10 GB/s. Network links are measured in bits: 10 GB/s × 8 = 80 Gbit/s. That is far beyond a few servers' network cards, which is why images are served from a CDN.
Numbers: Numbers to know.