Distorted Slider Images in Photo Book Theme

Hi:

I’m trying to use the Photo Book WordPress theme, but I’m having trouble with the slider images. The problem is the theme is resizing all of my images and they’re being distorted. If you go to https://blog.davidmcrews.com and compare the images in the slider to the corresponding thumbnails below it, you will see what I mean. Is there anything I can do to have the images displayed in the proper aspect ratio?