This short snippet restricts authors to only view the files from the media library which they have uploaded:

add_action('pre_get_posts','ml_restrict_media_library');
function ml_restrict_media_library( $wp_query_obj ) {
    global $current_user, $pagenow;
    if( !is_a( $current_user, 'WP_User') )
        return;
    if( 'admin-ajax.php' != $pagenow || $_REQUEST['action'] != 'query-attachments' )
        return;
    if( !current_user_can('update_core') )
        $wp_query_obj->set('author', $current_user->ID );
    return;
}

Add this part to your functions.php or include it in a seperate plugin

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