The image is from GypsyRock’s photostream. GypsyRock has been documenting San Francisco graffiti for some time, having amassed a photoset comprising 1110 photos.
What has always struck me about graffiti, throughout the world, is how essentially conservative it is. You might expect that such a transgressive medium would give birth to a chaotic range of expressioin, but in fact there are a few main styles that you see over and over again in different elaborations.
With such a large photoset, the graffiti depicted in GypsyRock’s images vary in quality, but some strikingly original and expressive examples are included.