Adding Alt Tag Column to Media Library List http://wordpress.stackexchange.com/questions/137082/adding-alt-tag-column-to-media-library-list

wp_admin_col_alt_tag.php

function wpse_media_extra_column( $cols ) {
    $cols["alt"] = "ALT";
    return $cols;
}
function wpse_media_extra_column_value( $column_name, $id ) {
    if( $column_name == 'alt' )
        echo get_post_meta( $id, '_wp_attachment_image_alt', true);
}
add_filter( 'manage_media_columns', 'wpse_media_extra_column' );
add_action( 'manage_media_custom_column', 'wpse_media_extra_column_value', 10, 2 );