using System;

​

using System.IO;

using System.Linq;

​

namespace TestApp

{

    class Program

    {

​

​

        static void Main(string[] args)

        {

            int counter = 1;

            DirectoryInfo d = new DirectoryInfo(Directory.GetCurrentDirectory());

            FileInfo[] infos = d.GetFiles("*.JPG").OrderBy(p => p.CreationTime).ToArray();

            foreach (FileInfo f in infos)

            {

                Console.WriteLine(String.Format("{0} change name to: {1}", f.FullName, String.Format("IMG_{0}.JPG", counter)));

                File.Move(f.FullName, String.Format("IMG_{0}", counter));

                counter++;

            }

            Console.WriteLine("Done");

        }

    }

}