This is a fun one. I was tinkering with using WEBP as the output format (not as a variant, but as the only output). Even my 2013-vintage Macbook Air can display them (Big Sur 11.6.8, Safari 15.6.1), so I suspect the number of visitors who can't view them is dwindling fast.
But when one uploads such an album to the jalbum.net hosting space, it can't extract a thumbnail image for the profile page. You can't even manually force it to do so after the upload, by "editing" the album.
Uploading "webp" to https://jefftucker.jalbum.net/webp/
Zip stream support detected
"webp" uploaded to https://jefftucker.jalbum.net/webp/ in 1.708s
Posting albumUrl: https://jefftucker.jalbum.net/webp/
Posting thumbnailUrl: https://jefftucker.jalbum.net/webp/thumbs/1929%20Packard%20633%205470.webp
java.io.IOException: Error while adding album. Server reported: Could not read album image. Not an image: url = https://jefftucker.jalbum.net/webp/thumbs/1929%20Packard%20633%205470.webp
All workers shut down
No problem within the app itself - the project thumbnail is correctly displayed in the project list. The integrated browser can't handle them, but that's a known problem.
I always start with the UI, then do the documentation (including the screenshots of the settings), then the template coding, and finally updating all the demo albums (which is a good sanity check - I follow it with a validation run).
Hmmmm.... I just tried to edit my (hidden) webp album, and I'm still getting the attached.
Feel free to meddle with that album.
There is no album.rss file in that album so the server doesn't know where the images are. (Though the server-generated album.rss used when a real file is missing should probably support webp too, which might not be the case.)