An nginx redirect based on user agents to an apology and a list of download links to WebP friendly browsers. I used to include a link to a Firefox fork that supported WebP natively, but no one bothered.
I made a sort of Google+ companion to the site which I'd bump them onto but I still haven't gotten the hang of not getting banned.
Yes, but not when storage, bandwidth, money, a desire to deliver only the best user experience (or nothing) and pushing WebP are concerns.
By the way, it's remarkable when running an image-heavy site how much bot/mass downloader traffic relative to humans vanish when turning away Firefox user agents.
I made a sort of Google+ companion to the site which I'd bump them onto but I still haven't gotten the hang of not getting banned.