Hi wjmdes — nice looking WP site you have there. ??
Those images are a bit different in proportion than the theme expects — actually, most WordPress themes, not just this one. For featured image use, generally something in a more balanced/proportional aspect ratio works best, say like 4:3 or similar.
What’s happening behind the scenes: the way WordPress crops images depends on how the theme registers “post thumbnail” sizes, and for Twenty Fourteen the minimum height for an image to be cropped is 372 pixels.
At 288 pixels high your images will be left uncropped and appear at their original aspect ratio as a result, though CSS rules exist to make them shrink to fit the container.
Now to even more geeky stuff! You can try to make it work by using your own CSS, either in a child theme or if you are running Jetpack plugin, use the Custom CSS function there.
.featured-content .post-thumbnail {
padding-top: 28.8%;
}
That will result in a layout something like this: https://cloudup.com/c0uFUEQSYZc