In photography, there is always a glass between the reality and the image. You can pick the focal length of the lens, you can pick a red filter to darken the sky, you can pick a polarizer to boost the contrast. Here is another one, the rainy glass, on the bus, after the rain, and is free of charge!

Every type of glass leaves its respective traces on the image. If one defines lens as the intermediate agent between reality and image, then it is obvious that we are all lens of some sorts. But then, what traces do we make on our images?