How to display alt tags in img src?

You are using the Advanced custom fields plugin.
The documentation for images: http://www.advancedcustomfields.com/resources/image/

To display the alt-tag for example, you can use this snippet:

$image = get_field('image');

if( !empty( $image ) ) {
    $alt = $image['alt'];
    ...
    echo '<img src="https://wordpress.stackexchange.com/questions/216629/..." alt=" . $alt .">'
}