Private VSTwain1 As New VintaSoftTwain()
Private imageCount As Integer


''' <summary>
''' Scans images asynchronously.
''' </summary>
Private Sub ScanImages()
    ' open the device manager
    If Not VSTwain1.DeviceManager_Open() Then
        Console.WriteLine(VSTwain1.errorString)
        Exit Sub
    End If

    ' open the device
    If Not VSTwain1.Device_Open Then
        Console.WriteLine(VSTwain1.errorString)
        Exit Sub
    End If

    ' scan images without UI
    VSTwain1.Device_ShowUI = False

    ' specify that device must save acquired images directly to disk
    VSTwain1.Device_TransferMode = TRANSFERMODE.TRANSFERMODE_File
    ' specify that acquired images must be save as JPEG files
    VSTwain1.Device_FileFormat = TWAINIMAGEFILEFORMAT.TWAINIMAGEFILEFORMAT_Jpeg
    ' specify the quality of JPEG images
    VSTwain1.Device_FileJpegQuality = 70
    ' initialize the image count
    imageCount = 1
    ' specify the name of file where acquired image must be saved
    VSTwain1.Device_FileName = Str(imageCount) + ".jpg"

    ' subscribe to the device events
    AddHandler VSTwain1.DeviceImageAcquired, AddressOf VSTwain1_ImageAcquired
    AddHandler VSTwain1.DeviceScanCompleted, AddressOf VSTwain1_ScanCompleted
    AddHandler VSTwain1.DeviceScanFailed, AddressOf VSTwain1_ScanFailed
    AddHandler VSTwain1.DeviceScanCanceled, AddressOf VSTwain1_ScanCanceled

    ' acquire images asynchronously
    VSTwain1.Device_AcquireImage()
End Sub

Private Sub VSTwain1_ImageAcquired()
    ' increment the image count
    imageCount = imageCount + 1
    ' specify the name of file where acquired image must be saved
    VSTwain1.Device_FileName = Str(imageCount) + ".jpg"
End Sub

Private Sub VSTwain1_ScanCompleted()
    Console.WriteLine("Scan is completed.")
End Sub

Private Sub VSTwain1_ScanFailed(errorString As String)
    Console.WriteLine(String.Format("Scan is failed: {0}.", errorString))
End Sub

Private Sub VSTwain1_ScanCanceled()
    Console.WriteLine("Scan is canceled.")
End Sub