Canonization candles were quite simply special candles offered by the Postulator of the Cause of the saint in question and they came decorated with depictions of the new saint and often scenes from their life as well. Generally they also depicted the arms of the bishop of the diocese from which the saint hailed as well as well as the arms of the pontiff under whom the saint was to be canonized. Three such candles would be presented during the ceremony, the largest of which was presented to the Prince Assistant to the Papal Throne -- a papal nobleman, another was presented to the pope himself, and the third to the Cardinal Prefect for the Congregation of the Causes for Saints.
A clearer view of such canonization candles can be seen here, taken from the canonization of St. Peter Claver in the year 1888, presented to Pope Leo XIII by Bishop Guglielmo Pifferi, Sacristan of the Apostolic Palace.
A still closer look shows the painted depiction of the saint (and another image of the same for comparison):