iTunes does not show podcast image

I cannot seem to get iTunes to display the image for my podcast. To be precise, iTunes doesn't even try to download the image for my podcast. Apache logs show the podcast and first audio file being downloaded by iTunes, but it is completely ignoring the <image> and <itunes:image> sections (shown here):

<image>
    <url><?php echo htmlentities($imageURL) ?></url>
    <title>My Podcast</title&g开发者_开发百科t;
    <link>http://<?php echo $_SERVER['HTTP_HOST'] ?></link>
    <width>300</width>
    <height>300</height>
</image>
<itunes:image>
    <url><?php echo $imageURL ?></url>
    <title>My Podcast</title>
    <link>http://<?php echo $_SERVER['HTTP_HOST'] ?></link>
</itunes:image>

I have also tried this slightly shorter alternative, with no luck.

<image>
    <url><?php echo $imageURL ?></url>
    <title>My Podcast</title>
    <link>http://<?php echo $_SERVER['HTTP_HOST'] ?></link>
    <width>300</width>
    <height>300</height>
</image>
<itunes:image href="<?php echo $imageURL ?>" />

A few notes:

• Yes the image URL works, but keep in mind that iTunes doesn't even try to download the image.
• This podcast is not listed in the iTunes Store.
• My iTunes is not connected with the iTunes Store.

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iTunes itself doesn't use the images set in the RSS feed (they're only used by the iTunes Store).

iTunes actually uses the cover art embedded in downloaded tracks (it appears to use the art from the newest track).

You can verify this by subscribing to a new podcast. You'll see its icon remains blank in the Podcasts listing in iTunes until a track has been downloaded, at which point the track cover art will be used for the podcast icon.