Cropping close to the window, eliminating sky, roof edge, and trees puts the main subject front and center. The square shape of the crop echoes the square shape of the window.
Crop to Show What's Important
Example: Cropping to focus on portion of image
From Jacci Howard Bear, About.com
Before: The bright blue sky and trees frame the building nicely but can also overshadow the tiny plant in the window. After: A close crop shows what the designer feels is most important about this photo.
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