A bird flew into the window here at work, I don't know when.
It was very challenging to get a photo of its impression, because it is very faint and I am working with a snapshot camera. I finally tricked the camera to stay in focus, then took a reference photo so that I could later reduce the intensity of the background and create contrast. However, the tree is moving in the wind and perfect subtraction is not possible.
Still, you can now see the ghostly image of the bird, including its wing tip in the upper right.