Capturar Captcha !!

Amigos vengo en busca de ideas para capturar un captchat de una web la etiqueta "img" no tiene el parametro ID los únicos parametros que tiene son el ancho y el alto, y lo otro es que el tipo de imagen que se muestra es ".png" no hay ninguna otra imagen en la web con esa extension, alguna idea de como podre capturarlo y mostrarlo en picturebox o webbrowser... ayuda...

encontre el siguiente ejemplo pero no lo entiendo bien si alguien pudiera desmenuzarlo un poco mas...

Código

 
'1) Put this Sub in your Project.
'You need:
 
'    PictureBox --> name = PictureBox1
'    WebBrowser --> name = WebBrowser1
 
 
'getcaptcha()
'Code:
Public Sub getcaptcha()
  Dim str As String = WebBrowser1.Document.GetElementById("recaptcha_image").InnerHtml 'Gets the html code for the recaptcha_image element
  Dim img As String = str.Remove(0, 33).Replace(""" width=300 height=57>", "") 'Deletes all the info around the link because the height and width will never change
  PictureBox1.ImageLocation = img 'Sets the ImageLocation to the URL of the ReCaptcha Image
    End Sub
 
'Then find the WebBrowser1 Document Completed Sub (shown below)
'Code:
Private Sub WebBrowser1_DocumentCompleted(ByVal sender As System.Object, ByVal e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
 
  End Sub
 
'And Add this code below to the Sub Above ^^
'Code:
If WebBrowser1.DocumentTitle.Contains("Emk") Then
    getcaptcha() 'Runs the sub getcaptcha()
  End If
 
'So it would look like this
'Code:
Private Sub WebBrowser1_DocumentCompleted(ByVal sender As System.Object, ByVal e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
 
    getcaptcha() 'Runs the sub getcaptcha()
 
  End Sub
 
'Read more: http://codertrick.blogspot.com/2011/07/get-captcha-image-in-picturebox-vbnet.html#ixzz1yo8AV2rM