ns-ext/image.optimize.csx

/*
            for %%i in (*.png) do pngquant %%i --force --output %%i --skip-if-larger
            for %%i in (*.jpg) do jpegtran -copy none -optimize -perfect %%i %%i
         *
         */


var files = Directory
    .EnumerateFiles(
        "./",
        "*.png",
        new EnumerationOptions
        {
            RecurseSubdirectories = true,
            AttributesToSkip = FileAttributes.ReparsePoint,
            IgnoreInaccessible = true
        }
    )
    .ToArray();

Parallel.ForEach(
    files,
    file =>
    {
        var startInfo = new ProcessStartInfo
        {
            FileName = "pngquant",
            Arguments = $"\"{file}\" --force --output \"{file}\" --skip-if-larger"
        };
        using var p = Process.Start(startInfo);
        p.WaitForExit();
        Console.WriteLine($"{file}: {p.ExitCode}");
    }
);

files = new[] { "*.jpg", "*.jpeg" }
    .SelectMany(
        x =>
            Directory.EnumerateFiles(
                "./",
                x,
                new EnumerationOptions
                {
                    RecurseSubdirectories = true,
                    AttributesToSkip = FileAttributes.ReparsePoint,
                    IgnoreInaccessible = true
                }
            )
    )
    .ToArray();

Parallel.ForEach(
    files,
    file =>
    {
        var startInfo = new ProcessStartInfo
        {
            FileName = "jpegtran",
            Arguments = $"-copy none -optimize -perfect \"{file}\" \"{file}\""
        };
        using var p = Process.Start(startInfo);
        p.WaitForExit();
        Console.WriteLine($"{file}: {p.ExitCode}");
    }
);