private static Image FitImage(Image image, Size size)
{
    Rectangle mask = new Rectangle(Point.Empty, size);
    float ratio = image.Width / (float)image.Height;
    float maskRatio = size.Width / (float)size.Height;

    if (size.Height * ratio > size.Width)
    {
        mask.Height = image.Height;
        mask.Width = (int)(image.Height * maskRatio);
        mask.X = (image.Width - mask.Width) / 2;
    }
    else
    {
        mask.Width = image.Width;
        mask.Height = (int)(image.Width * (1f / maskRatio));
        mask.Y = (image.Height - mask.Height) / 2;
    }

    Image screen = new Bitmap(size.Width, size.Height);
    using (Graphics graphics = Graphics.FromImage(screen))
    {
        graphics.DrawImage(image, new Rectangle(Point.Empty, size), mask, GraphicsUnit.Pixel);
        graphics.Flush();
    }

    return screen;
}