.order-content .wc_payment_method.payment_method_cod::before {
  content: url(../img/pay1.png);
}

.order-content .wc_payment_method.payment_method_liqpay-webplus::before {
  content: url(../img/pay2.png);
}

.order-content .wc_payment_method.payment_method_cheque::before {
  content: url(../img/pay3.png);
}