Digital Design & Imaging Service Inc. estimated around 200,000 people attended the rally, CBS News reported. Organizers on Saturday estimated 800,000.
Washington, D.C., metropolitan police have yet to release their own estimates.
The respected imaging firm uses balloons to fly cameras over events in order to estimate crowd size. The service said there was a margin of error of 15 percent for their estimation. The crowd size was largest at 1 p.m., the company said.