Comment by unilynx

Can whatever the next new image format for the web will be please have a JSON block at the start giving

  - dimensions
  - filetype 
  - minimum required decoder version
  - lossless: true/false
  - a list of alternative URLs and mimetypes to older image formats

And it doesn't have to be JSON, as long as it's in a fixed location (looking at you, AVIF and JPEG), extensible and can be decoded by just reading the first 8KB or 16KB.

Then any future image format is a simple drop-in without requiring complex processing on the server side or a lot of complexity in HTML (not to mention CSS)