If you are killed, you must be an insurgent!

I see news reports of ’50 insurgents killed’, ‘100 insurgents captured’ in various ‘operations’ currently in progress in Iraq (Operation Spear, Operation Dagger, etc.). How do they know that a person killed is an insurgent? Do insurgents wear any uniform or some identifying sign? Also, are the numbers reported in fifities, making them easy to remember and quote? I wonder.