How to resolve the error: An object reference is required for the non-static field, method or property in a C# console application?

I am writing a C# console application to merge 2 TIFF records into 1 merged file (multipage TIff image).

1 record is comprised of the front images of checks.

1 recorrd is comprised of the back images of checks.

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.


I am getting the error:
An object reference is required for the non-static field, method or property               'ReadBinary.BinaryFileTest.ConvertFromByteArray(byte[])'

---------

Byte[] img = bytes.Skip(irecpositionrevised + irectypelength).Take(intpos1revised).ToArray();
                   
Byte[] img1 = bytes.Skip(irecpositionrevised + irectypelength + intpos1revised).Take(intpos2revised).ToArray();
                   
MergeTwoImages(ConvertFromByteArray(img), ConvertFromByteArray(img1)); <--- error occurs here

private Image ConvertFromByteArray(byte[] input)
        {
            using (var ms = new MemoryStream(input))
            {
                return Image.FromStream(ms);
            }
        }

        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;
        }