Swift 4 (iOS 11+):

iOS 11 now supports images (only) to display in action buttons. You simply have to initialize a UISwipeActionsConfiguration object in your table view delegate object:

extension MyTableViewController:UITableViewDelegate {

    func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        
        let deleteAction = UIContextualAction(style: .normal, title:  nil, handler: { (ac:UIContextualAction, view:UIView, success:(Bool) -> Void) in
                
                debugPrint("Delete tapped")

                success(true)
            })

        deleteAction.image = UIImage(named: "icon_delete.png")
        deleteAction.backgroundColor = UIColor.red

        return UISwipeActionsConfiguration(actions: [deleteAction])
    }

}

Swift 4 (iOS 11+):

iOS 11 now supports images (only) to display in action buttons. You simply have to initialize a UISwipeActionsConfiguration object in your table view delegate object:

extension MyTableViewController:UITableViewDelegate {

    func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        
        let deleteAction = UIContextualAction(style: .normal, title:  nil, handler: { (ac:UIContextualAction, view:UIView, success:(Bool) -> Void) in
                
                debugPrint("Delete tapped")

                success(true)
            })

        deleteAction.image = UIImage(named: "icon_delete.png")
        deleteAction.backgroundColor = UIColor.red

        return UISwipeActionsConfiguration(actions: [deleteAction])
    }
}