Cropping the borders of image based on color in windows phone

Above is the image i am using. What i am trying to achieve is removing the red portion of the border from the image. How can I achieve this programmatically in windows phone? I found WriteableBitmapExtensions.Crop() method, but I am confused with the arguments (how i can find the x,y position of the image, as well as the size and the width?)

Also another issue I am facing is: I will get the images with differently sized borders, so I can't hardcode the x or y values.
Can anyone suggest a solution, or guide me to solve the issue?