And now, I feel darn special. I just identified a picture via a hidden reflection. Here's how.
This image was uploaded to Commons a few years ago. The author didn't specify where it was taken.
(click for larger version)
Now, it's immediately obvious that this is an MBTA Orange Line train, somewhere in Boston. (The Oak Grove rollsign confirms that). In the background we see catenary wire supports, thus this is a station on the Southwest Corridor between Back Bay and Forest Hills. The inbound (Oak-Grove-bound) train and the Amtrak tracks to the left indicate we're looking south, as do the shadows.
The white curved roof supports are the next clue; Bing Maps shows that only two stations have those support poles with the semi-open design. Those are Roxbury Crossing and Green Street. But there's no way to narrow it down any further; there's no background detail other than trees (which both stations have), and no station signs visible.
But wait. Zoom in on that image again. There's a lot of reflective surface visible: the train windows. And in the second window on the train, you can see a slightly-fuzzy station sign:
Let me flip that around for you, and brighten the image a bit for contrast:
Suddenly, you see it. The "ROSS" of "ROXBURY CROSSING" is visible. This is Roxbury Crossing station.
Lest you think I'm seeing more than I should in that fuzzy detail, I found a corroborating piece of evidence. Take a look at the concrete wall which separates the subway and mainline rail tracks. On the far right of the image, it terminates about at the last white column. At Green Street, the wall continues down onto the open platform.