ResizeAndFit

public static Image ResizeAndFit(this Image image, Size newSize)
{
    var sourceIsLandscape = image.Width > image.Height;
    var targetIsLandscape = newSize.Width > newSize.Height;

    var ratioWidth = (double)newSize.Width / (double)image.Width;
    var ratioHeight = (double)newSize.Height / (double)image.Height;

    var ratio = 0.0;

    if (ratioWidth > ratioHeight && sourceIsLandscape==targetIsLandscape)
        ratio = ratioWidth;
    else
        ratio = ratioHeight;

    int targetWidth = (int)(image.Width * ratio);
    int targetHeight = (int)(image.Height * ratio);

    var bitmap = new Bitmap(newSize.Width, newSize.Height);
    var graphics = Graphics.FromImage((Image)bitmap);
    
    graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;

    var offsetX = ((double)(newSize.Width - targetWidth)) / 2;
    var offsetY = ((double)(newSize.Height - targetHeight)) / 2;

    graphics.DrawImage(image, (int)offsetX, (int)offsetY, targetWidth, targetHeight);
    graphics.Dispose();

    return (Image)bitmap;
}

Image image = Image.FromStream(context.Request.InputStream).ResizeAndFit(new Size( 125, 100));