Portrait pictures and featured images

This has been puzzling me for the longest time and I wanted to ask if there was a way around this. I have a WordPress theme where you can set featured images. If I try setting a image that is portrait in size, all it does is just zoom in on the photo and it looks horrible. Is there any way to just have the picture be displayed at its normal size and not zoomed in once you set it as a featured image? Thank you