UPDATED#2:
Found it!
I'm attaching the latest version of the code which extracts the bits from the pattern image.
You will also need the pattern itself. I have isolated it in an uncompressed PNG, based on a clean screenshot from _Mike which was further enhanced by allesist, and I uploaded it here: https://i.imgur.com/dYQAd.png
Java code follows:
Code:
/*
Written by Sendatsu (12/09/2012) v1.2
http://www.ownedcore.com/forums/world-of-warcraft/
world-of-warcraft-general/375573-looking-inside-your-screenshots.html
*/
import java.awt.image.BufferedImage;
import java.io.*;
import javax.imageio.*;
public class Readwatermark
{
static final int pWidth=356; // Pattern width
static final int pHeight=240; // Pattern height
static final int pxWidth=4; // Pixels width
static final int pxHeight=5; // Pixels height
static final int bWidth=89; // Bits table width
static final int bHeight=48; // Bits table height
static final int Black=0xFF000000; // Black = 1 (yes, 1)
static final int White=0xFFFFFFFF; // White = 0 (yes, 0)
static final String filenameSrc = "pattern.png"; // Stores the filename
public static byte[][] getPatternBits(BufferedImage image)
{
byte barcode[][] = new byte[bWidth][bHeight]; // Stores the bits
for (int y=0, i=0; y<pWidth; y+=pxWidth, i++)
for (int x=0, j=0; x<pHeight; x+=pxHeight, j++)
if (image.getRGB(y+1,x)==Black)
// We check y+1 to target correctly (see pattern)
barcode[i][j]=1; // Got black (1)
else
barcode[i][j]=0; // Got white (0)
return barcode;
}
public static BufferedImage readImage(File file)
{
try
{
return (ImageIO.read(file));
}
catch (IOException e)
{
return (null);
}
}
public static void main(String[] args)
{
byte barcode[][]; // Stores the bits
File fileSrc = new File(filenameSrc); // Create file reference
BufferedImage imageSrc=readImage(fileSrc); // Read file
if (imageSrc==null)
System.exit(1); // No file found
barcode=getPatternBits(imageSrc); // Get bits
for (int i=0; i<bWidth; i++) // Print the pattern
for (int j=7; j<bHeight; j+=8) // 8 bits in a Byte
for (int k=j; k>=j-7; k--)
System.out.print(barcode[i][k]);
}
}
Notes:
a) the bits are 4x5: 1 is black and 0 is a white "space invader" that looks like this: https://i.imgur.com/o8Kcx.png)
b) the bits are stored top to bottom but you have to reverse them per 8s before you turn them into a byte (already in the code)
Feel free to use & extend and remember to reference source 
For those of you without a Java compiler, the output is this:
Code:
001100010011000000110111001101100011010000110010001100010011011000111001001000110011000111001001001101010100110101111110111011011001101110100101100101101110010110010111101101000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000011101100010010100010110111111110001101010011001010110011001011010001100011011011011011011001000001110010100000100000110011000011000011001111001011100101000000000000000000000000000000000000000001101011100101000111001110011010000110111000101100101001110100111000110110110111100001100000000000000000000000000000000000000000000000000000000000000000111111110011111100001111000000001111111111001010111111100011110011000111101011001100011110011101111011110111011000110001001100000011011100110110001101000011001000110001001101100011100100100011001100011100100100110101010011010111111011101101100110111010010110010110111001011001011110110100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001110110001001010001011011111111000110101001100101011001100101101000110001101101101101101100100000111001010000010000011001100001100001100111100101110010100000000000000000000000000000000000000000110101110010100011100111001101000011011100010110010100111010011100011011011011110000110000000000000000000000000000000000000000000000000000000000000000011111111001111110000111100000000111111111100101011111110001111001100011110101100110001111001110111101111011101100011000100110000001101110011011000110100001100100011000100110110001110010010001100110001110010010011010101001101011111101110110110011011101001011001011011100101100101111011010000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000111011000100101000101101111111100011010100110010101100110010110100011000110110110110110110010000011100101000001000001100110000110000110011110010111001010000000000000000000000000000000000000000011010111001010001110011100110100001101110001011001010011101001110001101101101111000011000000000000000000000000000000000000000000000000000000000000000001111111100111111000011110000000011111111110010101111111000111100110001111010110011000111100111011110111101110110
And once again, I can't thank you all enough for your help and support with this; especially you _Mike