how to get captcha image if src use java function? - vb.net

Question

How can I scrape captcha from this website
captchaImage.
I tried MSHTML but this website uses java script function to display retrieve captcha in it's src. Please try and answer me how can I achieve this.
Imports MahApps.Metro.Controls
Imports System.Net
Imports System.Windows.Forms
Class MainWindow
Inherits MetroWindow
Private Sub MetroWindow_Loaded(sender As Object, e As RoutedEventArgs)
wb.Navigate("https://www.irctc.co.in/eticketing/loginHome.jsf")
AddHandler wb.LoadCompleted, AddressOf wb_Loaded
End Sub
Private Sub btngo_Click(sender As Object, e As RoutedEventArgs) Handles btngo.Click
Dim htmldoc As MSHTML.IHTMLDocument2 = wb.Document
Dim usrtxtdoc As MSHTML.IHTMLElement = htmldoc.all.item("j_username", 0)
Dim usrpwddoc As MSHTML.IHTMLElement = htmldoc.all.item("j_password", 0)
Dim captchadoc As MSHTML.IHTMLElement = htmldoc.all.item("j_captcha", 0)
usrtxtdoc.innerText = txtusrname.Text
usrpwddoc.innerText = txtpwd.Text
captchadoc.innerText = txtcaptcha.Text
End Sub
Private Sub wb_Loaded(sender As Object, e As System.Windows.Navigation.NavigationEventArgs)
MsgBox("Loaded")
Dim htmldoc As MSHTML.IHTMLDocument2 = wb.Document
Dim htmldoc2 As MSHTML.HTMLDocument = wb.Document
Dim captchaimg As MSHTML.HTMLImg = htmldoc.all.item("cimage", 0)
Dim bitmap As New BitmapImage
bitmap.BeginInit()
bitmap.UriSource = New Uri(wb.FindResource("captchaImage"))
bitmap.EndInit()
imgcaptcha.Source = bitmap
End Sub
Private Sub wb_Navigated(sender As Object, e As NavigationEventArgs) Handles wb.Navigated
lblwbstatus.Content = "Load Completed"
End Sub
Private Sub wb_Navigating(sender As Object, e As NavigatingCancelEventArgs) Handles wb.Navigating
lblwbstatus.Content = "Navigating Please wait"
End Sub
Private Sub lblwbstatus_MouseDoubleClick(sender As Object, e As MouseButtonEventArgs) Handles lblwbstatus.MouseDoubleClick
wb.Refresh()
End Sub
End Class
you can download source from this link

Answer 1

Normally you would do this:
Dim htmldoc As mshtml.IHTMLDocument2 = wb.Document.DomDocument
Dim captchaimg As mshtml.HTMLImg = htmldoc.all.item("cimage", 0)
Dim imgRange As IHTMLControlRange = htmldoc.body.createControlRange()
For Each img As IHTMLImgElement In htmldoc.images
If img.nameProp = "captchaImage" Then
imgRange.add(img)
imgRange.execCommand("Copy", False, Nothing)
Using bmp As Bitmap = Clipboard.GetDataObject().GetData(DataFormats.Bitmap)
bmp.Save("c:\test.bmp")
End Using
End If
Next
However the image has an alpha channel that doesn't get copied to clipboard because of internet explorer issues (as you can read here Copying image from page results in black image).
Other ways are to check on internet explorer cache, but that image won't be cached because of HTTP headers, so you are out of luck.

Answer 2

the code above work very good with consideration -to the:
1- Item type- as in your webpage target example ("IMG").
2- the image proper name example: CaptchaImg.jpg to be written as CaptchaImg.jpg
3- add reference to (mshtml) and Imports mshtml into your project
4- right-Click reference on your project --> click add reference -->
-->Browse button click -choose or navigate to --->
C:\Windows\assembly\GAC\Microsoft.mshtml\7.0.3300.0__b03f5f7f11d50a3a\Microsoft.mshtml.dll
----> ok button click --- this will add Microsoft.mshtml.dll to your reference
finallt import to your project as (Imports mshtml).
5- change the directory bmp.Save("c:\test.bmp")---> to for example bmp.Save("c:\test\test.bmp")
for security and administration right privileged.