|Image courtesy of Daily Mail UK Circled areas show "slinky" effect common to moving crowds.|
|Distance courtesy Google. About 3400 feet.|
|Width of street is about 111 feet.|
Crowd estimate using the standard one person for every 10 square feet (moving crowd) is 34,000-to-40,000 ...not 800,000
To provide a reference point, the average NCAA Div I football game had 42,200 paying attendees. So the parade in Washington DC pulled as many attendees as the average East Carolina, Pittsburgh or UC-Fresno home football game (Source)
I analyzed the shadow of the Washington Monument that was in the un-cropped picture and deduced that the image was taken at approximately 10:45 in the morning. The shadow is approximately 490 feet long at the time the image was taken. Since the event did not officially start until noon, and ended after 2:00 PM, the number of attendees was certainly higher than the 34,000-to-40,000 estimated in the blog.
One highly credible source placed the attendance around 180,000.
In my defense, I am not the person who posted a picture of 34,000 people and presented it as evidence that 800,000 people were in attendance.
Apologies for any sleep you may have lost.