there has been a growing recognition of its value as an art form. There have been major exhibitions of street art in galleries in Paris, London and Los Angeles. American artist Elura Emerald organised a street art exhibition at a New York Gallery in 2008. She defended street artists, saying "artists who paint on the street are merely expressing themselves, not hurting anyone. They should be appreciated and celebrated". Who are the Artists? Most street artists are anonymous, but others have become globally famous. Here are three stars of the street art world: Os Gemeos are identical twin brothers from Sao Paulo in Brazil. They paint everything from tags to huge, colourful pictures of people on the sides of buildings. Their work is often so big that they need cranes to help them work. In 2007, they covered the whole of a castle in Scotland with paint. Blek le rat started out painting rats on the walls of his home city, Paris. Nowadays, he tries to make people think about different social issues and problems. He paints pictures of homeless people in big cities to encourage residents to think about the problem of homelessness. Faith 47 is from Cape Town in South Africa. She paints big, colourful pictures of people and animals and likes to explore different locations. Her work is found on pavements, in empty factories and on abandoned cars. She likes the fact that most street art is temporary and will soon be removed by weather or cleaners