Reni was much influenced by Alexander Allori called Bronzino, his first master, and many works attributed to the latter were in fact by his hand.
Jean de Boulogne, a gifted imitator of Caravaggio, copied a painting by Reni, which was eventually sold on the advice of Pierre Mignard as a genuine Reni to the brother of King Louis 14th. The monarch, who was eventually informed about such trick, finally said that Boulogne should have better tried to produce works believed to be by Reni rather than his own.
Mignard himself deceived his rival Le Brun with an imitation of Reni, an artist who in fact had a great influence over many 17th Century painters in France and in Italy.
Some of these painters, such as Andrea Pozzo, Carlo Maratta or Nicolo Berettoni produced works, which were eventually authenticated as being by Reni. Maratta was in turn copied by Luigi Gazzi and Lazzaro Baldi while Michel Corneille, a French painter, was accustomed to copying works by the Carracci brothers.
Another most copied artist was Caravaggio who had numerous followers such as Jean Valentin, Manfredi, Nicolas Régnier, G. Seghers, Evaristo Baschenis, Orazio Gentileschi, Domenico Tati or Ribera.
GREAT MASTERS OFTEN COPIED OTHERS
Luca Giordano was not only a copyist but also a much gifted forger. At 13, he used to copy works by Michelangelo, Raphael, Amerighi or Pietro da Cortona. Giordano notably sold many of these copies pretending they had been produced by such masters. He also sold a painting reputedly as by Bassano to King Carlos II of Spain and admitted later that it was a forgery but the monarch did not complain and praised him instead.
Giordano also painted a copy of a painting, "The Adoration of the Magi" by Dürer but his patron decided to sue him on learning of such trick. A Neapolitan court in charge of that case however congratulated Giordano who also had many imitators such as Frederico Crivelli, Anselmo Gabriel, Giuseppe Simonelli or Solimena.