compatible with 3.9.1 yet ?

I think there is a misunderstanding. This is not a widget. And it will not display any images in an RSS widget, that doesn’t fetch images from the feed.

The RSS Image Feed just adds an image to your RSS feed.

And it works up to WP 4.0.

Ok, I tried doing the same thing using the RSS widget. How do I display the feed with images on my sidebar then?

I’m sorry. But I’ll have to say the same thing. It just adds an image to your RSS feed.

So, if you want your feed (or another) with images in your widget, you’ll have to get a plugin that fetches and displays images in an RSS widget, as the standard RSS widget doesn’t do that.