How to create an image from a 2-dimensional byte array?

If it's a rectangular array (i.e. a byte[,]) instead of a jagged array (byte[][]) then you may be able to do it pretty simply with some unsafe code.

Have a look at my parallel Mandelbrot set generation code - only the bottom bit is interesting, where it constructs a Bitmap from a palette and a block of data:

byte[] data = query.ToArray();

unsafe
{
    fixed (byte* ptr = data)
    {
        IntPtr scan0 = new IntPtr(ptr);
        Bitmap bitmap = new Bitmap(ImageWidth, ImageHeight, // Image size
                                   ImageWidth, // Scan size
                                   PixelFormat.Format8bppIndexed, scan0);
        ColorPalette palette = bitmap.Palette;
        palette.Entries[0] = Color.Black;
        for (int i=1; i < 256; i++)
        {
            palette.Entries[i] = Color.FromArgb((i*7)%256, (i*7)%256, 255);
        }
        bitmap.Palette = palette;
        // Stuff
    }
}

I don't know whether you can unpin the array after constructing the bitmap - if I were using this for production code I'd look at that more closely.

If you want the byte arrays to be processed inorder, you can do the following

byte[][] doubleArray = GetMyByteArray();
byte[] singleArray = doubleArray.SelectMany(x => x).ToArray();
MemoryStream ms = new MemoryStream(singleArray);
System.drawing.Image im = Image.FromStream(ms);

The SelectMany method essentially takes the arrays of arrays and returns the elements in order. Starting with the first element of the first array, finishing that array and then moving onto the next. This will continue until all elements are processed.