Using C#, how would you convert var type variables to image type variables to pass to a function?

I am writing a C# console application that generates 2 files in binary format.

1 file is comprised of the front images of checks.

1 file is comprised of the back images of checks.

Do you know how I could modify this code (in particular the Function call) to merge these 2 TIFF files together into 1 TIFF file (called a multipage TIFF image)?

I want to give the user the ability to read the front image of a particular check image and then read the back image of the same check.

The img variable contains the front images of checks.
The img1 variable contains the back images of checks.
------------------

var img = bytes.Skip(irecpositionrevised + irectypelength).Take(intpos1revised).ToArray();

var img1 = bytes.Skip(irecpositionrevised + irectypelength + intpos1revised).Take(intpos2revised).ToArray();

MergeTwoImages(img, img1)  <--------  This will not work because the data type needs to be converted


public static Bitmap MergeTwoImages(Image firstImage, Image secondImage)
{
if (firstImage == null)
{
      throw new ArgumentNullException("firstImage");
}

if (secondImage == null)
{
      throw new ArgumentNullException("secondImage");
}

int outputImageWidth = firstImage.Width > secondImage.Width ? firstImage.Width : secondImage.Width;

int outputImageHeight = firstImage.Height + secondImage.Height + 1;

Bitmap outputImage = new Bitmap(outputImageWidth, outputImageHeight, System.Drawing.Imaging.PixelFormat.Format32bppArgb);

using (Graphics graphics = Graphics.FromImage(outputImage))
{
     graphics.DrawImage(firstImage, new Rectangle(new Point(), firstImage.Size),
               new Rectangle(new Point(), firstImage.Size), GraphicsUnit.Pixel);
     graphics.DrawImage(secondImage, new Rectangle(new Point(0, firstImage.Height + 1), secondImage.Size),    
               new Rectangle(new Point(), secondImage.Size), GraphicsUnit.Pixel);
}

return outputImage;
}