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class ConfigWrapper
{
    public static double LowerBound { get { return double.Parse(ConfigurationManager.AppSettings["LowerBound"].ToString()); } }
    public static double UpperBound { get { return double.Parse(ConfigurationManager.AppSettings["UpperBound"].ToString()); } }
    ...
}

 ...

var face = allFaces.Where(f => f.Proportion > lowerBound && f.Proportion < upperBound).ToList()
                   .OrderBy(f => f.Proportion).ThenByDescending(f => f.Rectangle.Height).FirstOrDefault();
OutputImage(file, face);

OutputImage(file, allFaces.Where(f => 
    f.Proportion > double.Parse(ConfigurationManager.AppSettings["LowerBound"].ToString()) && 
    f.Proportion < double.Parse(ConfigurationManager.AppSettings["UpperBound"].ToString())).ToList()
        .OrderBy(f => f.Proportion)
        .ThenByDescending(f => f.Rectangle.Height)
        .FirstOrDefault());

phil.o wrote:

Thanks for asking.