Portfolio image cuts into square

I uploaded a picture (portait 600 x 900 px) and I select it as featured image. But when I view the portfolio item (go to the “page”) the (featured) image is cut into a square. So the top and bottom is just removed.
This happens whit every portrait-format image I upload and I have tried to make new portfolio items but it doesn’t change.

I just want the image in a portfolio-item-page to be portrait and not be cut. Can I insert image in some other way (not featured)?