Hi extuid,
There seems no way to override the Joomla to generate custom RSS content.
Though, you have two options for this problem.
1. Insert image in your article content (intro text)
2. Overwrite joomla com_content core file (not recommended)
By opening componentscom_contentviewsfeaturedview.feed.php
And add this block code
if(!empty($row->images) && is_string($row->images)){
$images = json_decode($row->images);
$description = '<img src="' . $images->image_intro . '" />' . $description;
}
just before
// Loads item info into rss array
$doc->addItem($item);
You also need to do the same with componentscom_contentviewscategoryview.feed.php
Hope it helps,
Regards