How many people attended Obama's inauguration? A post on TechCrunch shows a beautiful satellite image with enormous crowd in Washington. You can almost count people standing there. Can you?
I've tried to count people on the image. First, cropped the picture to ease the work, most of the people are in this croped image anyway. Then added a layer in GIMP and roughly painted with white paint over crowded areas.

Then added another layer, black one, to get a clear view of crowded area.

A histogram showed that white area is 34,6% percent of whole picture. But what is the size of the whole real area? I used Google Maps to count this and it seemed that the area is about 12879429,99 feet square.

A one person standing in the crowd occupies about 2,5 feet square (I googled this info). So now all I needed to do is to calculate
12879429,99 feet square / 2,5 feet square *34,6%
And now I know: there were about 1782513 people on Obama's inauguration in Washington.