// Create a CIRandomGenerator filter with the input image
var random_generator = new CIRandomGenerator ();

// Get the altered image from the filter
var output = new CICrop {
	Image = random_generator.OutputImage,
	Rectangle = new CIVector (0, 0, 400, 300)
}.OutputImage;

// To render the results, we need to create a context, and then
// use one of the context rendering APIs, in this case, we render the
// result into a CoreGraphics image, which is merely a useful representation
//
var context = CIContext.FromOptions (null);

var cgimage = context.CreateCGImage (output, output.Extent);

// The above cgimage can be added to a screen view, for example, this
// would add it to a UIImageView on the screen:
myImageView.Image = UIImage.FromImage (cgimage);