C# Random Image from Directory [duplicate]

This question already has an answer here:

• Why does Random.Next() always return the same number 7 answers

I am attempting to retrieve a random image from a directory and display it on a page. It works in essence but when I am trying to get more than one random image they are always the same! However if I debug the code and set through slowly it picks different ones. Any ideas on what I am missing here?

Class File:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.IO;

/// <summary>
/// Summary description for Photos
/// </summary>
public class Photos
{

    #region Variables

    private const string m_sImagesFolder = "/images/random/";

    #endregion

    #region Enums

    public enum PhotoType
    {
        Portrait,
        Landscape
    }

    #endregion

    public Photos()
    {
        //
        // TODO: Add constructor logic here
        //
    }

    public string GetRandomPhoto(PhotoType pt)
    {
        return GetRandomPhoto(pt, m_sImagesFolder);
    }

    public string GetRandomPhoto(PhotoType pt, string sImagesFolder)
    {

        string sFile = null;
        string[] sExtensions = new string[] { ".png", ".jpg", ".gif" };

        if (!sImagesFolder.EndsWith("/"))
            sImagesFolder += "/";

        switch (pt)
        {

            case PhotoType.Portrait:
                sImagesFolder += "portrait/";
                break;

            case PhotoType.Landscape:
                sImagesFolder += "landscape/";
                break;

        }

        string sImagesFolder_Local = HttpContext.Current.Server.MapPath(sImagesFolder);

        try
        {
            DirectoryInfo di = new DirectoryInfo(sImagesFolder_Local);
            var rgFiles = di.GetFiles("*.*").Where(f => sExtensions.Contains(f.Extension.ToLower()));
            Random R = new Random();
            sFile = rgFiles.ElementAt(R.Next(0, rgFiles.Count())).Name;
        }
        // Probably should only catch specific exceptions throwable by the above methods.
        catch
        {

        }

        if (sFile != null)
            sFile = sImagesFolder + sFile;

        return sFile;

    }

}

Calling Page:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class academy_information_Gifted : System.Web.UI.Page
{

    protected void Page_Load(object sender, EventArgs e)
    {

        // Get random photos
        Photos p = new Photos();
        img1.Attributes["src"] = p.GetRandomPhoto(Photos.PhotoType.Portrait);
        img2.Attributes["src"] = p.GetRandomPhoto(Photos.PhotoType.Portrait);

    }

}