By default the thumbnail images (the small images in a gallery) are square/cropped. This makes them all the same size which makes them easy to arrange nicely in a gallery. However you can show the original dimensions of the images if you wish.
- Login to your Control Panel
- Click ‘Pages’ -> Edit
- Find the page for which you want to unsquare the thumbnails for and click 'Edit Details'
- Scroll all the way down and set 'Square Image Thumbnails' to 'No'
- Click ‘Save changes’