C#

private Bitmap DistortImage(Image sourceImage,Point TopLeft, Point TopRight, Point BottomLeft, Point BottomRight)
{
    int width, height; //The destination bitmap size

    width = Convert.ToInt32(Math.Max(p2.X, p4.X));
    height = Convert.ToInt32(Math.Max(p3.Y, p4.Y));

    Bitmap dest = new Bitmap(width, height);
    Bitmap src = new Bitmap(sourceImage);

    //Start the loop

    //Loop down the left border
    for (int yStart = TopLeft.Y; yStart < BottomLeft.Y; yStart++)
    {
        //Find where the left most part is
        double xStart = TopLeft.X + (((double)(yStart - TopLeft.Y) / (double)(BottomLeft.Y - TopLeft.Y) * (BottomLeft.X - TopLeft.X)));
        //Find the x and y position corrisponding on the right border
        double yEnd = TopRight.Y + ((double)(yStart - TopLeft.Y) / (double)(BottomLeft.Y - TopLeft.Y)) * (BottomRight.Y - TopRight.Y);
        double xEnd = TopRight.X + (((double)(yEnd - TopRight.Y) / (double)(BottomRight.Y - TopRight.Y) * (BottomRight.X - TopRight.X)));

        //How stretched this line is
        double xScale = (xEnd - xStart) / (double)src.Width;

        //Loop through the line and draw according to it
        for (double x = xStart; x < xEnd; x+= xScale)
        {
            double y = yStart + (((double)(x - xStart) / (double)(xEnd - xStart) * (yEnd - yStart)));
            //How stretched the line is vertically
            double yScale =   ((double)(x - xStart) / (double)(xEnd - xStart)) / ((double)(BottomLeft.Y - TopLeft.Y) / (double)(BottomRight.Y - TopRight.Y));

            //Find out what src pixel this will use
            double ySrc = ((double)(yStart - TopLeft.Y) / (double)(BottomLeft.Y - TopLeft.Y)) * src.Height;
            double xSrc = ((double)(x - xStart) / (double)(xEnd - xStart)) * src.Width;

            //Find out how many pixels we are responsible for drawing
            int xNumPixels, yNumPixels;
            xNumPixels = Convert.ToInt32(Math.Ceiling(xScale));
            yNumPixels = Convert.ToInt32(Math.Ceiling(yScale));

            int yNumPixelsAbove;
            yNumPixelsAbove = Convert.ToInt32(Math.Ceiling(yNumPixels / 2d));

            if (xSrc < 0)
                xSrc = 0;
            if (ySrc < 0)
                ySrc = 0;

            //The source pixel
            Color col = src.GetPixel(Convert.ToInt32(Math.Floor(xSrc)), Convert.ToInt32(Math.Floor(ySrc)));

            //Draw all the pixels needed
            for (int sx = Convert.ToInt32(Math.Floor(x)); sx < Convert.ToInt32(Math.Floor(x)) + xNumPixels; sx++)
            {
                if (sx < width)
                {
                    for (int sy = Convert.ToInt32(Math.Floor(y)) - yNumPixelsAbove; sy < Convert.ToInt32(Math.Floor(y)) + yNumPixels; sy++)
                    {
                        if (sy >= 0 && sy < height)
                            dest.SetPixel(sx, sy, col);
                    }
                }
            }
        }
    }

    src.Dispose();
    src = null;

    return dest;
}