c# winforms corner detectors

I need a c# class that has a method that accepts and image and returns an image. Windows XP a winform is round at the two top corners and square at the bottom 2 corners. Windows Vista is round on all corners. Windows 7 is round on all corners. Yahoo messenger version 10 is round on the top corners and square on the bottom like XP. Let me be clear I am looking for an edge detector. If the corner is round I trim it and it needs to be transparent. I do not want something that just tries to do it based on the OS type. I already have that. I need something that can look at that image and determind by color of the corners and decide to crop it or not. It will have to work on rectangular images only. It must detect the corner based on color, it can use any edge detector or corner detector that you want to implement. I do not want a third party library to do this. Thanks and good luck bidding.