You need to swap left and right images to use the cross-eyed method on these. You can try downloading as an image, use an app like Preview to Flip Horizontal (that will work).

Otherwise you're seeing a kind of inverse stereo image.

(EDIT: Having said that, I tried a few of the images and the stereo effect is subtle. The soldier on the horse — I was not even able to get that to "snap" for me. I am not great with cross-eyed stereo though.)