c#不使用系统api实现可以指定区域屏幕截屏功能

//保存图象文件
        private void SaveImage(Image image)
        {
            if (saveFileDialog.ShowDialog(this) == DialogResult.OK)
            {
                string fileName = saveFileDialog.FileName;
                string extension = Path.GetExtension(fileName);
                if (extension == ".jpg")
                {
                    image.Save(fileName, ImageFormat.Jpeg);
                }
                else
                {
                    image.Save(fileName, ImageFormat.Bmp);
                }
            }
        }
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