Here is a suggestion for styling your background image with both height and width properties:
.bg {
/* Location of the image */
background-image: url(images/background-photo.jpg);
/* Centering the background image vertically and horizontally */
background-position: center center;
/* Prevent the background image from tiling */
background-repeat: no-repeat;
/* Fix the background image in the viewport to prevent movement when content exceeds image height */
background-attachment: fixed;
/* Make the background image rescale based on container size */
background-size: cover;
/* Set a background color to display while the image is loading */
background-color: #464646;
}