Does a negative drug test mean you are clean from drugs? pictures? explanation.

Not necessarily: A drug test can have false negative results: sometimes a person can add chemicals to a urine sample to "hide" the drugs you are testing for. Sometimes people can substitute another person's urine or dilute urine. There are ways to get around a urine drug test. A sophisticated during testing facility will witness the provision of a urine sample and maintain the integrity of the chain of possession.