public partial class Form1 : Form
    {
        const int SRCCOPY = 0xcc0020;

        [DllImport("gdi32.dll")]
        public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hObjectSource, int nXSrc, int nYSrc, int dwRop);


        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

            Bitmap btm_1 = (Bitmap)pictureBox1.Image;
            Bitmap btm_2 = (Bitmap)pictureBox2.Image;

            Graphics srcG = Graphics.FromImage(btm_1);
            Graphics dstG = Graphics.FromImage(btm_2);
            IntPtr srcPtr = srcG.GetHdc();
            IntPtr dstPtr = dstG.GetHdc();

            BitBlt(dstPtr, 0, 0, btm_1.Width, btm_1.Height, srcPtr, 0, 0, SRCCOPY);

            srcG.ReleaseHdc(srcPtr);
            dstG.ReleaseHdc(dstPtr);
            srcG.Dispose();
            dstG.Dispose();

            pictureBox2.Refresh();

        }
    }