You can't, you have to trust the archiver, as with anything in Nostr.
Discussion
Well, now we trust the internet archive don't we?
We are the archivers now.
Attestations provide WoT for events; in this case web archives.
Well yes, that's their whole service though. They are used because people trust them. We need to provide at least as much confidence as them.
There's no reason a service(s) couldn't coexist alongside or within a network of individuals. Said services could even recruit contributors from the wider network, or make a service out of "verifying" and storing network events that they deem "accurate", on their own relays. The 2 things would help create accountability for both.
But at that point, that service needs to render and download the page. Then they need to compare it to the page downloaded by the user. You can't use a comparison operator or anything because on most pages, it will vary based on the user and device. You would need manual review and judgement calls by the reviewer which will have to check word by word to see if anything is removed or added, then for display they will have to decide if differences in presentation are valid or not.
Basically, checking a page uploaded by another user is far more laborious and complex than just capturing it yourself.
The far more likely scenario if this is implemented is, there will not be a separate service verifying pages uploaded by global users, but those services will be the ones capturing and uploading the sites. So the user will still just tell these guys a link for them to screenshot, but there will be multiple competing services that the user can choose from, and they will all be interoperable from multiple clients.
While any npub can post a capture, all the clients will curate the captures based on the trustability of the npub and your captures won't be used for anything but curious people looking up shit for reference. Most clients will work on a fully whitelist basis, only showing captures from a few selected npubs, banning them at the first sign of forgery.
This is still better than the internet archive, but you will never see crowdsourced web captures that are worth shit to anyone.
The NIP on attestations that nostr:nprofile1qqsvfa085adgecmg84ffelcxx6zrn3ffu5jrc6cjtwng0zge3ptv43cpz9mhxue69uhkummnw3ezuamfdejj7qgcwaehxw309anxjmr5v4ezumn0wd68ytnhd9hx2tcwmah2e developed addresses this issue. Originally for proof of place but has been generalized. Ultimately you have to trust the attestor.
I would view one person archiving a webpage differently than many people archiving that same webpage.
But web pages are often served differently to different visitors. There can be location /personalization variations of exactly the same page. Even to different logged-out, “anonymous” users.
Also, a “page” is more than a single page, there are usually dozens of associated files like css, js, and images. Just saving the html won’t get you very far when you want to look at it again later.
you could normalize some params like browser engine, agent, javascript on/off, timezone, language, etc.
it would probably won't match exactly as you probably have trackers and different scripts
that's why you have multiple sources (archivers).