static void Main(string[] args)
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));
Console.WriteLine("Done");