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