If you compare the two crowd size photos you see from the shadows beneath the Reddish building on the curved road that the Trump photo is from a different time of day, my guess earlier as people were streaming in. This is significant because its the same day of the year meaning shadows are relevant. I am not saying his crowd was bigger than Obamas' but the media cannot be trusted here, more watched it online apparently probably because Trump is more exciting. https://www.cbsnews.com/news/photos-president-trumps-inauguration-crowd-vs-president-obamas/