Ask HN: Counting # of protestors?

I was at the anti-trump rally in Los Angeles today. The LAPD estimated the crowd size to be 8,000 however that number seemed very low to me. I'm wondering if anyone has some software than can look at footage to estimate crowd size. There are a few shots that capture the majority of the protest today like this: https://instagram.com/p/BMuxQDcjdI4/

Would love to have a hard count of how many ppl were there - not an estimation!