No, the images are never cropped, they are just resized while keeping the original aspect ratio untouched. Please note that the resize feature works only for the original image, not for the thumbnails generated by WordPress.
There is one exception, and that is the use of Smart Cropping. If you have enabled the "Enable SmartCrop" and "Resize large images" options, your original images may be cropped. For more information about this, please see this article.
You can find more details about how the resize feature works here.