Global news agency Agence France-Presse published an image of lightning striking the basilica's dome on Monday, which it said was taken "on the day the Pope" announced his resignation.
AFP said the striking image was captured by photographer Filippo Monteforte, who works for Italian national news and photo agency ANSA.
Benedict announced his resignation in Latin during a meeting of Vatican cardinals, calling it "a decision of great importance for the life of the church."
He emphasized that carrying out the duties of being pope requires "both strength of mind and body."
The Vatican stressed that no specific medical condition prompted Benedict's decision to quit, the first pontiff to do so in 600 years. The move surprised even his closest aides, even though Benedict, 85, had made clear in the past he would step down if he became too old or infirm.
The Vatican newspaper, L'Osservatore Romano, said he had made up his mind nearly a year ago after trips to Mexico and Cuba tired him out.
His 89-year-old brother, Georg Ratzinger, said: "Age is weighing on him. My brother would like more rest at this age."
As one can imagine, many are speculating on social media and elsewhere that the lightning strike may have been a sign of negative or positive approval from God.