I thought it was neat how when putting the full image URL into archive.org, they would report whether they had the specific image cached. e.g. The image link http://img1.jurko.net/avatar_2288.gif which has been dead 10 or so years can be viewed using https://web.archive.org/web/20171126042 ... r_2288.gif .
Although it would technically work, I wouldn't want to throw unnecessary load onto archive.org servers by literally replacing the dead http://img1.jurko.net/avatar_2288.gif link with https://web.archive.org/web/20171126042 ... r_2288.gif .
But I thought this might be an interesting phpBB extension. To crawl one's own phpBB forum, and for any now-dead image links that are found, see if archive.org happens to have a copy. And if there is an archived copy of the image, upload that archived image to phpBB's own image store, and replace the dead link with the now-local URL reference.
Maybe, this should even have the option to be a "constant" function. Not the archive.org part, but an option for phpBB to process every
[img]type reference as soon as it's created and posted. And to upload the image into phpBB's own local image store, even before the image might become unavailable online. And then be able to refer to that local copy if and when the remote image host is no longer available.
Which looks like pretty much the opposite of what most existing extensions or mods out there did, which seem to be all about making it easier to upload attachments directly to third-party host services, rather than your local phpBB board.
Obviously it's opt-in, and would only be attractive to customers who like the idea of exchanging storage space for reliable images that don't disappear at the whim of some third-party advertisement-supported hosting service that goes out of business without notice.
But I would definitely use both aspects: Attempt resolving existing dead links using WayBackMachine, and prevent future dead links by creating "shadow uploads" that can be used if and when the remote host's image starts being unavailable.