How would I add to add an icon to my RSS feed XML file

I don't use RSS feed readers personally anymore, but upon request I have setup a simple RSS file in XML that users can subscribe to. When I checked it out on Feedly, I saw that some other feeds have "logos" for next to the feed's name. I did some internet search and read that the <image> tag can be used for that, but my RSS feed still doesn't show the logo,

So, how would I add a logo like the other sides (below the first row in the screenshot) did? (Note that I replaced the actual contents by "...", because I don't want to advertise anything here)

The current way I was trying to add the logo is:

<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0">
<channel>

<image>
    <url>http://.../logo_rssfeed.gif</url>
    <title>...</title>
    <link>...</link>
</image>

<item>
<title>...</title>
<link>...</link>
<guid>...</guid>
<pubDate>19 Jun 2014</pubDate>
<description>
...
</description>
</item>

...
</channel>
</rss>

Link to the source code of my RSS feed

I believe the site icons in Feedly and many other readers are actually favicons. To get an icon displayed, you need to add a favicon to your main site. As a bonus you'll get the favicon to show up for people who bookmark your site or add it to sites like Delicious and more.

Also, you should make sure your feed is valid. It's not that difficult if you follow these recommendations and will help feed readers show your content correctly. The consequence of this is obviously higher engagement and subscribers from RSS.