It's incredibly simple. The NFT points to a URL controlled by the author. The author configured the web server so that it would respond with different images "based on the IP or User Agent of the requester." There's nothing web3 or blockchain going on here, it's just a normal image URL where the web server responds differently for different requests. Kinda like image hosting services that would return a placeholder image if you tried to hotlink directly to the image URL.
It's incredibly simple. The NFT points to a URL controlled by the author. The author configured the web server so that it would respond with different images "based on the IP or User Agent of the requester." There's nothing web3 or blockchain going on here, it's just a normal image URL where the web server responds differently for different requests. Kinda like image hosting services that would return a placeholder image if you tried to hotlink directly to the image URL.