The top photo toppling the statue was a staged event for the Western media.
The crowd cheering were Iraqis (Northern Kurds) brought in for the event while troops blocked off the perimeter so they could film. They didn't have near enough people so they pulled in for a tight shot. It happens all the time in film making. We've shot seens where we can take 50 extras and rotate them in such a way to give the impression of a crowd of thousands.
I've seen longshots of the 2nd photo though, and those crowds looked pretty authentic to me.
I don't know how many actually burned US flags though. There were a few, but the footage could easily have been misleading, in that they were only a few isolated cases of it, and not the huge outpouring of anti-US sentiment as much of the media is claiming.