If you want to display an image on the lock screen from your page, you cannot do this, only iOS applications. If you want to play music in the background (while the safari is closed, not killed), you can do it like this:
var mp3 = document.createElement("audio"); mp3.setAttribute('src', 'http://example.com/track.mp3'); mp3.load(); document.documentElement.appendChild(mp3); mp3.play(); mp3.pause()
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