polygon crop an image

Hey

I've spent quite a time trying to find out a way to crop images exclusively in unity3d and I found good libraries that helps with that. But the problem was that I wanted to crop not square/rectangular shape but an unidentified geometric shape defined by four points (polygon) and even with that I managed to find a usage of the "System.Drawing" library which gave the result that I was looking for.

The only issue is that it's not supported in an Android phone.

I've been looking into OpenCV but it's a huge library and I'm not a total expert in Java, so I was hoping if anyone knows a more simpler image cropping library that helps serving this purpose.

Thanks in advance.