Convert bitmaps to one multipage TIFF image in .NET 2.0

Start with the first bitmap by putting it into an Image object

Bitmap bitmap = (Bitmap)Image.FromFile(file);

Save the bitmap to memory as tiff

MemoryStream byteStream = new MemoryStream();
bitmap.Save(byteStream, ImageFormat.Tiff);

Put Tiff into another Image object

Image tiff = Image.FromStream(byteStream)

Prepare encoders:

var encoderInfo = ImageCodecInfo.GetImageEncoders().First(i => i.MimeType == "image/tiff");

EncoderParameters encoderParams = new EncoderParameters(2);
encoderParams.Param[0] = new EncoderParameter(Encoder.Compression, (long)EncoderValue.CompressionNone);
encoderParams.Param[1] = new EncoderParameter(Encoder.SaveFlag, (long)EncoderValue.MultiFrame);

Save to file:

tiff.Save(sOutFilePath, encoderInfo, encoderParams);

For subsequent pages, prepare encoders:

EncoderParameters EncoderParams = new EncoderParameters(2);
EncoderParameter SaveEncodeParam = new EncoderParameter(
     Encoder.SaveFlag, 
     (long)EncoderValue.FrameDimensionPage);
EncoderParameter CompressionEncodeParam = new EncoderParameter(
     Encoder.Compression, (long)EncoderValue.CompressionNone);
EncoderParams.Param[0] = CompressionEncodeParam;
EncoderParams.Param[1] = SaveEncodeParam;
tiff.SaveAdd(/* next image as tiff - do the same as above with memory */, EncoderParams);

Finally flush the file:

EncoderParameter SaveEncodeParam = new EncoderParameter(
     Encoder.SaveFlag, (long)EncoderValue.Flush);
EncoderParams = new EncoderParameters(1);
EncoderParams.Param[0] = SaveEncodeParam;
tiff.SaveAdd(EncoderParams);

That should get you started.

Necromancing
The accepted answer is a bit vague.
Here's full working code:

public class MultiPageTiff
{


    private static System.Drawing.Imaging.ImageCodecInfo GetEncoderInfo(string mimeType)
    {
        System.Drawing.Imaging.ImageCodecInfo[] encoders =
            System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();

        if (encoders != null)
        {
            for (int i = 0; i < encoders.Length; i++)
            {
                if (encoders[i].MimeType == mimeType)
                {
                    return encoders[i];
                } // End if (encoders[i].MimeType == mimeType) 
            } // Next i 

        } // End if (encoders != null) 

        return null;
    } // End Function GetEncoderInfo 


    public static System.Drawing.Image Generate(string[] filez)
    {
        System.Drawing.Image multiPageFile = null;
        byte[] ba = null;


        System.Drawing.Imaging.ImageCodecInfo tiffCodec = GetEncoderInfo("image/tiff");


        using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
        {
            for (int i = 0; i < filez.Length; ++i)
            {
                using (System.Drawing.Image inputImage = System.Drawing.Image.FromFile(filez[i]))
                {

                    using (System.IO.MemoryStream byteStream = new System.IO.MemoryStream())
                    {
                        inputImage.Save(byteStream, System.Drawing.Imaging.ImageFormat.Tiff);

                        if (i == 0)
                        {
                            multiPageFile = System.Drawing.Image.FromStream(byteStream);
                            multiPageFile = SaveImages(tiffCodec, ms, multiPageFile, null);
                        }
                        else
                        {

                            using (System.Drawing.Image tiffImage = System.Drawing.Image.FromStream(byteStream))
                            {
                                multiPageFile = SaveImages(tiffCodec, ms, tiffImage, multiPageFile);
                            } // End Using tiffImage 

                        }
                    } // End Using byteStream 

                } // End Using inputImage 

            } // Next i 

            ba = ms.ToArray();
        } // End Using ms 

        System.IO.File.WriteAllBytes(@"d:\mytiff.tiff", ba);

        //if (multiPageFile != null)
        //{
        //    multiPageFile.Dispose();
        //    multiPageFile = null;
        //}

        return multiPageFile;
    }


    private static System.Drawing.Image SaveImages(
          System.Drawing.Imaging.ImageCodecInfo tiffCodec
        , System.IO.MemoryStream outputStream
        , System.Drawing.Image tiffImage, System.Drawing.Image firstImage)
    {


        using (System.Drawing.Imaging.EncoderParameters encParameters =
              new System.Drawing.Imaging.EncoderParameters(3))
        {

            if (firstImage == null)
            {
                encParameters.Param[0] = new System.Drawing.Imaging.EncoderParameter(
                    System.Drawing.Imaging.Encoder.SaveFlag
                    , (long)System.Drawing.Imaging.EncoderValue.MultiFrame // 18L 
                );
            }
            else
            {
                encParameters.Param[0] = new System.Drawing.Imaging.EncoderParameter(
                    System.Drawing.Imaging.Encoder.SaveFlag
                    , (long)System.Drawing.Imaging.EncoderValue.FrameDimensionPage // 23L
                );
            }

            encParameters.Param[1] = new System.Drawing.Imaging.EncoderParameter(
                System.Drawing.Imaging.Encoder.ColorDepth, 24L
            );


            encParameters.Param[2] = new System.Drawing.Imaging.EncoderParameter(
                System.Drawing.Imaging.Encoder.Compression
                , (long)System.Drawing.Imaging.EncoderValue.CompressionLZW
            );


            if (firstImage == null)
            {
                firstImage = tiffImage;

                ((System.Drawing.Bitmap)tiffImage).SetResolution(96, 96);
                firstImage.Save(outputStream, tiffCodec, encParameters);
            }
            else
            {
                ((System.Drawing.Bitmap)tiffImage).SetResolution(96, 96);

                firstImage.SaveAdd(tiffImage, encParameters);
            }

            if (encParameters.Param[0] != null)
                encParameters.Param[0].Dispose();

            if (encParameters.Param[1] != null)
                encParameters.Param[1].Dispose();

            if (encParameters.Param[2] != null)
                encParameters.Param[2].Dispose();

        } // End Using encParameters 

        return firstImage;
    }


}

Not being a fan of Microsoft's track record when it comes to handling and creating files of standardized formats, I would suggest using ImageMagick, available as a .Net library in the form of MagickNet (beware, http://midimick.com/magicknet/ currently has a spyware popup, I have alerted the site owner).

Here is how to do this in vb.net:

Imports System.Drawing.Imaging

Sub CreateTiff(sOutTiffFile As String, sInFile1 As String, sInFile2 As String)
    Dim bitmap As Bitmap = Image.FromFile(sInFile1)
    Dim byteStream As MemoryStream = New MemoryStream()
    bitmap.Save(byteStream, System.Drawing.Imaging.ImageFormat.Tiff)

    Dim tiff As Image = Image.FromStream(byteStream)

    Dim oParams As EncoderParameters = New EncoderParameters(2)
    oParams.Param(0) = New EncoderParameter(Imaging.Encoder.Compression, EncoderValue.CompressionCCITT4)
    oParams.Param(1) = New EncoderParameter(Imaging.Encoder.SaveFlag, EncoderValue.MultiFrame)
    tiff.Save(sOutTiffFile, GetEncoderInfo("image/tiff"), oParams)

    'Next Page
    Dim bitmap2 As Bitmap = Image.FromFile(sInFile2)
    oParams.Param(1) = New EncoderParameter(Imaging.Encoder.SaveFlag, EncoderValue.FrameDimensionPage)
    tiff.SaveAdd(bitmap2, oParams)

    'Flush 
    Dim oFlushParams As EncoderParameters = New EncoderParameters(1)
    oFlushParams.Param(0) = New EncoderParameter(Imaging.Encoder.SaveFlag, EncoderValue.Flush)
    tiff.SaveAdd(oFlushParams)
End Sub

Private Function GetEncoderInfo(mimeType As String) As System.Drawing.Imaging.ImageCodecInfo
    Dim encoders = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders()
    For i As Integer = 0 To encoders.Length - 1
        If encoders(i).MimeType = mimeType Then
            Return encoders(i)
        End If
    Next
    Return Nothing
End Function