In mine the hash is encoded as z-base-32 and namespaced with an uncommon first character:

  $ publish example.png
  https://example.com/+umk3cm5cah5akbqeueq8914zimfktoih

And for when it matters, the filename can optionally be attached:

  $ publish --named example.png
  https://example.com/+umk3cm5cah5akbqeueq8914zimfktoih
  $ http --headers 'https://example.com/+umk3cm5cah5akbqeueq8914zimfktoih' | grep 'Content-Disposition'
  Content-Disposition: inline; filename="example.png"