Google is your best friend. you can make use of it...
still these links can help you ...
image resize and cropping[
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Cropping Particular Region In Image Using C# [
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Cropping Images[
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simple way is
Image img = Image.FromFile("d:\\yourimage.jpg");
Bitmap bmp= new Bitmap(img);
Bitmap crop= bmp.Clone(new Rectangle(100, 100, 300, 300), bmpImage.
PixelFormat);
crop.Save("d:\\yourimage1.jpg");