You must use Shapes.AddPicture rather than Pictures.Insert:
Sub InsertPictures()
   Dim strPath                     As String
   Dim strFile                     As String
   Dim objPic                      As Shape
   Dim LastRow                     As Long
   Dim i                           As Long

   LastRow = Cells(Rows.Count, "A").End(xlUp).Row

   If LastRow = 1 Then
      MsgBox "No data is available...", vbInformation
      Exit Sub
   End If

   Application.ScreenUpdating = False

   strPath = "C:\Users\user\Desktop\"

   If Right(strPath, 1) <> "\" Then strPath = strPath & "\"

   For i = 2 To LastRow
      strFile = Cells(i, "A").Value & ".jpg"
      If Len(Dir(strPath & strFile, vbNormal)) > 0 Then
         With Cells(i, "B")
            Set objPic = ActiveSheet.Shapes.AddPicture(Filename:=strPath & strFile, linktofile:=msoFalse, _
                                                       savewithdocument:=msoCTrue, Left:=.Left, _
                                                       Top:=.Top, Width:=.Width, Height:=.Height)
            objPic.LockAspectRatio = msoFalse
         End With
      Else
         Cells(i, "B").Value = "N/A"
      End If
   Next i

   Application.ScreenUpdating = True

End Sub