Art or vandalism?

You probably already have seen some drawings scattered around the streets. Also known as graffiti or graffiti.
The only problem is that sometimes people do not know how to differentiate art from vandalism. Usually Graffiti is done in public areas or on property walls with the permission of the owner, not counting his form, which displays lush and well made drawings.
The opposite of the graffiti, which is a great vandalism. Made just to offend or "rip off" with nonsensical gibberish and insinuations to drugs and profanity.