Answer by Jeff_Alieffson for How do I add an image to an item in RSS 2.0?

One of solutions is to use CDATA in description

<![CDATA[  Image inside RSS<img src="http://example.com/img/smiley.gif" alt="Smiley face">  ... further content ...   ]]>       

Note, that you may have a problem with hotlink prevented site.