gistfile1.cs

var image = new Bitmap(100, 100, PixelFormat.Format24bppRgb);

using (var locked = image.Lock()) unsafe
{
	for (var x = 0; x < image.Width; x++)
		for (var y = 0; y < image.Height; y++)
			if (y == image.Height / 3)
				image.SetPixel(x, y, Color.FromArgb(70, 0, 0));
}

using (var graphics = new Graphics(image))
{
	graphics.DrawImage(image, 100, 100);
}