That 10.8 wallpaper you linked looks original. 3200 x 2000 appears to be the original resolution for Lion and Mountain Lion (also note how the version on this site is cropped).
10.8 is less obvious so hard to say with 100% certainty, but if you look at, say 10.6 it's super obvious.
If you look at the bright star at the top left, in the original it has a clean lens flare. In the version from this site, the diagonal flare has a zebra stripe pattern. This is characteristic of AI upscaling of a very thin diagonal line.
10.8 is less obvious so hard to say with 100% certainty, but if you look at, say 10.6 it's super obvious.
Here's the original wallpaper shipped by Apple: https://cdn.osxdaily.com/wp-content/uploads/2009/08/defaultd... Here's the one from this site: https://512pixels.net/downloads/macos-wallpapers-6k/10-6-6k....
If you look at the bright star at the top left, in the original it has a clean lens flare. In the version from this site, the diagonal flare has a zebra stripe pattern. This is characteristic of AI upscaling of a very thin diagonal line.