When you lock an iphone after using safari / chrome etc., when an mp3 file is playing, it displays blank artwork and a hard link to the mp3 file location, which looks quite ugly
You can add a string that will be shown on the iOS lockscreen by setting a title
attribute on your element. It's all on the "song" line, so it doesn't look totally native, but it gets your point across.
I don't, however, know of any way to coax iOS into displaying album art of media coming from a browser.