MOSCOW --- Does the size of a crowd matter? Only if you're trying to gauge the stability of Vladimir Putin's rule and the strength of the opposition.

After the historic Dec. 10 protest against parliamentary elections, no one could agree on the number of people who attended, and commentators with different political views cited widely varying figures to support their views of the event's importance. Publicly available aerial photos were limited, and some international publications could only report that "tens of thousands"...