Save image using System.IO in C#

<table> <tr> <td>Uploaded Image </td> <td> <asp:FileUpload ID="fil1" runat="server"/> </td> </tr> <tr> <td colspan="2" align="center"> <asp:Button ID="btnsubmit" runat="server" Text="Submit" CssClass="btn" OnClientClick="StartProgressBar()" OnClick="btnsubmit_Click"/> </td> </tr> <tr> <td colspan="2" align="center"> <asp:Label ID="lblmessage" CssClass="lbl" runat="server"></asp:Label> </td> </tr> </tr> </table>

protected void btnsubmit_Click(object sender, EventArgs e)     {         try         {             HttpPostedFile Myimage;             Myimage = fil1.PostedFile;             if (Myimage.ContentLength == 0)             {                 lblmessage.Text = "Please Upload Image.";             }             else             {              if (Path.GetExtension(Myimage.FileName).ToLower() == ".jpg" || Path.GetExtension(Myimage.FileName).ToLower() == ".png" || Path.GetExtension(Myimage.FileName).ToLower() == ".gif" )                {                 int bytesval = fil1.PostedFile.ContentLength;                 int kilobytesval = bytesval / 1024;                 System.Threading.Thread.Sleep(2000);                                   fil1.PostedFile.SaveAs(@"E:\ images\" + GenerateString() + "" + Path.GetExtension(Myimage.FileName));                 lblmessage.Text = "Image saved successfully" + kilobytesval + " KB <br>";              }              else              {                  lblmessage.Text="Invalid Image Format. The Image Extension Must Be .jpg.";              }             }         }         catch (Exception ex)         {             lblmessage.Text = ex.ToString();         }     }     public string GenerateString()     {         string allowedChars = "a,b,c,d,e,f,g,h,j,k,m,n,p,q,r,s,t,u,v,w,x,y,z,";         allowedChars += "A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z,";         allowedChars += "2,3,4,5,6,7,8,9";         char[] sep = { ',' };         string[] arr = allowedChars.Split(sep);         string passwordString = "";         string temp;         Random rand = new Random();         for (int i = 0; i < 6; i++)         {             temp = arr[rand.Next(0, arr.Length)];             passwordString += temp;         }         return passwordString;     }