static bool _isScanningFinished;

/// <summary>
/// Job counter.
/// </summary>
static int _jobCounter = -1;



/// <summary>
/// Asynchronously acquires images from TWAIN device and detects end of batch job.
/// </summary>
public static void AsynchronouslyAcquireImageFromTwainDeviceAndDetectEndOfBatchJob()
{
    _isScanningFinished = false;

    // create the device manager
    using (Vintasoft.Twain.DeviceManager deviceManager = new Vintasoft.Twain.DeviceManager())
    {
        deviceManager.IsTwain2Compatible = true;
        // open the device manager
        deviceManager.Open();

        // get the device
        Vintasoft.Twain.Device device = deviceManager.DefaultDevice;
        if (device == null)
            return;

        // subscribe to the device events
        device.ImageAcquired += new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
        device.ScanCanceled += new System.EventHandler(device_ScanCanceled);
        device.ScanFailed += new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
        device.ScanFinished += new System.EventHandler(device_ScanFinished);

        // set scanning settings
        device.TransferMode = Vintasoft.Twain.TransferMode.Memory;
        device.ShowUI = true;

        // open the device
        device.Open();
        // specify that job separator must be searched and scanned
        device.JobControl = Vintasoft.Twain.JobControl.DetectAndIncludeJobSeparatorAndContinueScanning;
        // increment job count
        _jobCounter = _jobCounter + 1;

        // acquire images asynchronously
        device.Acquire();

        // wait while feeder will be stopped
        while (!_isScanningFinished)
        {
            System.Windows.Forms.Application.DoEvents();
        }
    }
}

/// <summary>
/// Image is acquired.
/// </summary>
private static void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
{
    Vintasoft.Twain.Device device = (Vintasoft.Twain.Device)sender;
    // if job separator is detected
    if (device.EndOfJob)
        // increment job count and do not save the job separator image
        _jobCounter = _jobCounter + 1;
    // if job separator is NOT detected
    else
        // add image to the multipage TIFF file for current job
        e.Image.Save(string.Format(@"d:\job{0}.tif", _jobCounter));

    // dispose the acquired image
    e.Image.Dispose();
}

/// <summary>
/// Scan is canceled.
/// </summary>
private static void device_ScanCanceled(object sender, System.EventArgs e)
{
    System.Console.WriteLine("Scan is canceled.");
}

/// <summary>
/// Scan is failed.
/// </summary>
private static void device_ScanFailed(object sender, Vintasoft.Twain.ScanFailedEventArgs e)
{
    System.Console.WriteLine(string.Format("Scan is failed: {0}.", e.ErrorString));
}

/// <summary>
/// Scan is finished.
/// </summary>
private static void device_ScanFinished(object sender, System.EventArgs e)
{
    Vintasoft.Twain.Device device = (Vintasoft.Twain.Device)sender;

    // unsubscribe from device events
    device.ImageAcquired -= new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
    device.ScanCanceled -= new System.EventHandler(device_ScanCanceled);
    device.ScanFailed -= new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
    device.ScanFinished -= new System.EventHandler(device_ScanFinished);

    // if device is not closed
    if (device.State != Vintasoft.Twain.DeviceState.Closed)
        // close the device
        device.Close();

    System.Console.WriteLine("Scan is finished.");

    _isScanningFinished = true;
}

Shared _isScanningFinished As Boolean

''' <summary>
''' Job counter.
''' </summary>
Shared _jobCounter As Integer = -1



''' <summary>
''' Asynchronously acquires images from TWAIN device and detects end of batch job.
''' </summary>
Public Shared Sub AsynchronouslyAcquireImageFromTwainDeviceAndDetectEndOfBatchJob()
    _isScanningFinished = False

    ' create the device manager
    Using deviceManager As New Vintasoft.Twain.DeviceManager()
        deviceManager.IsTwain2Compatible = True
        ' open the device manager
        deviceManager.Open()

        ' get the device
        Dim device As Vintasoft.Twain.Device = deviceManager.DefaultDevice
        If device Is Nothing Then
            Return
        End If

        ' subscribe to the device events
        AddHandler device.ImageAcquired, New System.EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
        AddHandler device.ScanCanceled, New System.EventHandler(AddressOf device_ScanCanceled)
        AddHandler device.ScanFailed, New System.EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
        AddHandler device.ScanFinished, New System.EventHandler(AddressOf device_ScanFinished)

        ' set scanning settings
        device.TransferMode = Vintasoft.Twain.TransferMode.Memory
        device.ShowUI = True

        ' open the device
        device.Open()
        ' specify that job separator must be searched and scanned
        device.JobControl = Vintasoft.Twain.JobControl.DetectAndIncludeJobSeparatorAndContinueScanning
        ' increment job count
        _jobCounter = _jobCounter + 1

        ' acquire images asynchronously
        device.Acquire()

        ' wait while feeder will be stopped
        While Not _isScanningFinished
            System.Windows.Forms.Application.DoEvents()
        End While
    End Using
End Sub

''' <summary>
''' Image is acquired.
''' </summary>
Private Shared Sub device_ImageAcquired(sender As Object, e As Vintasoft.Twain.ImageAcquiredEventArgs)
    Dim device As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)
    ' if job separator is detected
    If device.EndOfJob Then
        ' increment job count and do not save the job separator image
        _jobCounter = _jobCounter + 1
    Else
        ' if job separator is NOT detected
        ' add image to the multipage TIFF file for current job
        e.Image.Save(String.Format("d:\job{0}.tif", _jobCounter))
    End If

    ' dispose the acquired image
    e.Image.Dispose()
End Sub

''' <summary>
''' Scan is canceled.
''' </summary>
Private Shared Sub device_ScanCanceled(sender As Object, e As System.EventArgs)
    System.Console.WriteLine("Scan is canceled.")
End Sub

''' <summary>
''' Scan is failed.
''' </summary>
Private Shared Sub device_ScanFailed(sender As Object, e As Vintasoft.Twain.ScanFailedEventArgs)
    System.Console.WriteLine(String.Format("Scan is failed: {0}.", e.ErrorString))
End Sub

''' <summary>
''' Scan is finished.
''' </summary>
Private Shared Sub device_ScanFinished(sender As Object, e As System.EventArgs)
    Dim device As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)

    ' unsubscribe from device events
    RemoveHandler device.ImageAcquired, New System.EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
    RemoveHandler device.ScanCanceled, New System.EventHandler(AddressOf device_ScanCanceled)
    RemoveHandler device.ScanFailed, New System.EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
    RemoveHandler device.ScanFinished, New System.EventHandler(AddressOf device_ScanFinished)

    ' if device is not closed
    If device.State <> Vintasoft.Twain.DeviceState.Closed Then
        ' close the device
        device.Close()
    End If

    System.Console.WriteLine("Scan is finished.")

    _isScanningFinished = True
End Sub