My images in K2 articles are not sizing automatic.

I have a K2 article with an intro text, then the read-more divider.

In the second part I have an article that was imported from an rss feed.

For this article I've been playing with setting the image size in the right hand panel to x-large and x-small, but the image stays the same.

The image is not stored on my own website, but on the one where the article comes from.

 

Any idea why the image isn't resizing?

The image resizing is for K2 item images which you select and upload. At that time there are several sized created and when there is one present and the settings are correct it will show in the size you select.