I could just use 10 different URLs for each NFT. All pointing to the same image. I can also use 10 different wallets to obfuscate it more. For that matter, I can use different blockchains as well.
Now it’s 10 completely different NFTs pointing to the same image. To verify there are no duplicates, you need to check every NFT in existence (across all blockchains in existence).
I could just use 10 different URLs for each NFT. All pointing to the same image. I can also use 10 different wallets to obfuscate it more. For that matter, I can use different blockchains as well.
Now it’s 10 completely different NFTs pointing to the same image. To verify there are no duplicates, you need to check every NFT in existence (across all blockchains in existence).