Overcast skies afford better photos

The sky looked great today on my way to the train station. Typically I'd be dealing with Summer blue skies which make photos fairly boring, but today the sky looked ominous. I stopped off at Bryant Park and snapped a few photos using just my iPhone 4S.

I shot them using Camera Plus and simply used the clarity filter. Does anyone know of an app that would fix the horizon line? It's especially noticeable in the second photo.

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