It is NOT illegal for you to post pictures that you took of someone else using any type of drugs on the internet. HOWEVER it IS illegal for you to not report a crime (in this case somebody using drugs) and not report it. Therefore by posting these pictures you could possibly get all of the people that used the drugs put in jail, but you yourself could also go to jail along with these people if they get caught and the police figure out that you didn't report it happening.
