I could probably count on one hand the number of people who would find this guide useful since most people really don't care about the white headmasters and if they do they are much more likely to plop down the $100 or so bucks on the KO's than spend thousands trying to track down the originals. However, for that small subset of people who are actually looking for the real thing, I hope this helps in identifying any unscrupulous sellers out there.
So let me start out with physical observations and descriptions. Obviously the biggest difference is the KOs do not have the copyright stamp on them. But if you can't get the seller to take a picture of the stamp or perhaps you don't speak the language of the auction site (thanks Yahoo Japan) there are a few other signs. The KO versions are a slightly different color of white than the real things. They are a bit more "creamy" in color, almost like that of skim milk, whereas the originals are a very solid white. I took all these pictures on a black background to try and highlight the differences better. These things are notoriously hard to photograph but I hope the pictures are different enough so you can see the variations.
So in the pictures above the originals look a little more yellow, which I think is due to the light around my lightbox. Nevertheless, they are a very clean white in person, notice how the KOs are a brilliant white, that translates to more "creamy" is the best way I can describe it.
On to the individual figures, unfortunately I am still missing a white Loafer so I can't compare him.
Kirk is possibly the best example I have because his photo came out so clear. Here you can really see the detail differences. Also, I wanted to include an example of the head mode just for posterity, notice the absent copyright on the KO. You'll also notice on the front of the head the KO is missing the two indention lines that run vertically down on either side of the face. This is most likely because of the recasting process.
I know these aren't big details and really won't matter to most people, but if there are any collectors out there who are searching for the genuine items I hope this aids you and prevents you from being the victim of any sellers trying to sell the KOs as originals.
There are more comparison pictures on the following posts:
Grail Find! Headmaster Rodney's White Counterpart
Wait, what? There's another one?
The White Lione
The final figure: White Headmaster Shuffler