Locating the end points of a bridge-like structure in an image

Question

How do I locate the end points of a bridge-like structure in an image?

Below is a generalized representation.

Answer 1

You could also try running a moving window over the image with a filter that is sum of the pixel values inside. Tune the size to say double the size of the bridge width. You should expect to see a fairly sharp transition when you run off the bridge onto the shore.