Counting
One of the responsibilities of an occupying power under the Geneva convention is to keep a record of all civilian casualties. The US has not done this during it's occupation of Iraq, citing among other things, difficulties in keeping a tally.I don't think anyone expects such a record to be perfect, just an honest attempt to keep track. Claiming it's difficult is no excuse.
It may not even be that hard. Raed Jarrar has compiled a list of casualties during the war using the efforts of Iraqi volunteers.
Someone really wants to ask Bush or Cheney why this isn't being done.