Is it possible that images in a RSS-feed can be used with Getfeed?
I don't see a reason why not. Try calling the snippet with your feed, without the &tpl property, to see what data is available to you based on your feed.
Since different feeds return different placeholders, what is best to get the placeholders available is to pass getFeed without a 'tpl' parameter. This will then show you an array of fields and their values. Their 'indexes', or the key of each array item, can be used in a placeholder.