This Sunday: London in Pictures Earlier this week, I was at Yale doing portfolio reviews and crits of the work of M.F.A. photography students, while on the lookout for new talent for the magazine. More than once, the photographers discussing their work would talk about aiming for ambiguity in a photograph. But an artist should never aim for ambiguity, I told them. A photographer should try to present something clear, deliberate. Let the viewer decide later if an image is rich with layers of meaning, and multiple readings, and therefore, ambiguous. Of course this was the weekly magazine photo editor in me speaking. In our trade, we aim for clarity. And to be clear, the work of the Yale M.F.A. students was very impressive overall. When brainstorming covers, we try to boil a subject down to its essence so that we can compose an image that clearly conveys what the story is about. The ultimate goal is temptation - to entice the reader into opening the issue. This week's cover isn't clear. It requires a stare down. Upon first look, it seems to be a pencil sketch. There are many layers to it. There is movement and a mesmerizing, lyrical energy to the image. Ferris wheels start to form, and then the London Eye emerges. The image on the cover is by Idris Khan, an artist we'd been eager to work with and were quick to call upon when forming the line-up for the London issue. His pictures often involve the layering of previously existing images. For one series, he represented musical scores by layering every sheet of music in a composition. Here is Mozart's "Requiem," as seen through Khan's lens: In his 2006 piece, "Caravaggio.....The Final Years," Khan brought together the late work of the artist Michelangelo Merisi da Caravaggio. And in "Blossfeldt.... After Karl Blossfeldt "Art Forms in Nature"" 2005, Khan combined all the photographs of Karl Blossveldt into one picture. For our London issue, we knew we would want to show the city, but without repeating the usual cliches. Khan seemed like the sort of artist who could do something new with well-worn imagery. He told us that he wanted to collect postcards of the places that tourists photograph over and over and over - Big Ben, the Houses of Parliament, Tower Bridge, the London Eye - and layer them to form new images. It was an idea he had already been mulling; a serendipitous meeting of our journalistic needs and his artistic obsessions. When he sent us his initial sketches, we knew we were on our way to a very unusual, and very ambiguous cover. Several of these London pictures commissioned by The New York Times Magazine, will be exhibited as 30 by 40 inch prints at the Armory Show that opens this Thursday, March 8 and runs through Sunday, March 11.