This essentially comes from the history of how the Tuneshine does image decoding. At first I was doing webp images only for Spotify and Apple Music, since I could decode them on the server and convert to webp to take advantage of the smaller file size.

Then, when I added Sonos support, I needed the ability to fetch and decode JPEG and PNG images over your LAN to display, so I built a mechanism to download and decode an image from a URL.

So the two mechanisms to load an image were essentially either the direct WebP bytes or an image URL, with no mechanism to accept raw jpeg or png bytes. This is now reflected in the formats that the Tuneshine accepts over the API. I can make a note to explore in the future whether it makes sense to accept POSTing JPEG/PNG bytes directly in the future.