You don't really need a higher entropy. It's enough to have a strong enough shade, so the shaded part loses enough color information that when you undo the shade that part looks posterized. That way an "attacker" needs to work a lot more on the picture, as it's not easy to add the lost color information again without adding a blur to that part.
Looks like the background is adaptive:
http://www.gettyimages.com/detail/photo/chiufen-village-high...
Yes, they clearly thought thru the white-image issue:
http://www.gettyimages.com/detail/photo/ice-extreme-close-up...
The box is just a low-contrast region (not adaptive). But I still think there will be lots of conditions where it will be tough to read. http://www.gettyimages.com/detail/photo/chess-board-royalty-...
If you register and log in, you get a watermark-free image. It even suggests this on the image info page...
Re:Getty's New Watermark
by AndrewNoNumbers on Saturday May 26, 2012 @02:03PM
(#4027899)
You, sir, are clearly thinking like an engineer.
Also, it looks fairly easy for an "unfair use"-er to "heal" the watermark away. They should consider a watermark with higher entropy. (like a stipple-shaded box or one with subtle random variation in shade around the box edge.)