Extract one object from set of objects

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I want to extract one leaf from bunch of leaves to detect its features. So first I tried to find edges of the image and extract one object, but it seems that this way is not going to work. What I want to do is just extract one leaf from an image taken in real environment of the plant (See the following example image)

As an example consider I want to cut off the leaf marked with red line. Then I can proceed to identify features of that leaf. Can any one please suggest a step by step method to do this. I'm using C++ as the language.

Thank you in advance.