using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        List<string> allThePaths = new List<string>()

        {

            "c:\\somedir\\1.jpg",

            "c:\\somedir\\2.jpg",

            "c:\\somedir\\20.jpg",

            "c:\\somedir\\7.jpg",

            "c:\\somedir\\12.jpg",

            "c:\\somedir\\8.jpg",

            "c:\\somedir\\9.jpg",

            "c:\\somedir\\3.jpg",

            "c:\\somedir\\10.jpg"

        };

​

        List<string> sortedPaths = allThePaths

            .OrderBy(stringItem => stringItem.Length)

            .ThenBy(stringItem => stringItem).ToList();

​

        foreach (var path in sortedPaths)

        {

            Console.WriteLine(path);

        }

    }

}