Using system.IO;

Text box with ID=Textbox1
Button with ID= button1
Label with ID= label1

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
 
public partial class _Default : System.Web.UI.Page
{ 
protected void Page_Load(object sender, EventArgs e)
{ 
if (IsPostBack) 
doesFileExist(TextBox1.Text);
}
 
public void doesFileExist(string searchString)
{ 
if (TextBox1.Text != "")
{ 
string imageFolder;
imageFolder = Server.MapPath("/media/") + searchString.ToString();
if (File.Exists(imageFolder))
{ 
Label1.Text = "File <b>" + searchString + "</b> <u>does</u> exist in '/media/' folder.";
}
else
{ 
Label1.Text = "File <b>" + searchString + "</b> <u>does not</u> exist in '/media/' folder.";
}
}
else 
Label1.Text = "Please enter some text.";
}
}