Everybody goes to l'Osservatore Romano for photographs of papal events. But don't forget to visit Foto Felici, too! Especially if you have an interest in old papal photos. See their site here:
Founded in Rome in 1863, Foto Felici is one of the oldest photo shops in the world. Their family has recorded 150 years of Rome and Vatican history under 11 pontificates, from Blessed Pius IX to Benedict XVI. And the business is still in the Felici family, even today.
The Felici photo archives contain an estimated 100,000 images of Rome at the end of the nineteenth century on glass slide negatives, 2,000 views of Italy from the beginning of the twentieth century and millions of photos on film and glass negatives as well as now digital memory documenting the activities of the popes and Vatican life.
Visit their shop, just a few minutes walk from the Vatican City on the Via Cola di Rienzo.