The four photographers, one of whom works for the French news agency AFP, were arrested while covering the huge protests that took place in Istanbul in March.
Hundreds of thousands of people gathered in the streets to show their dissatisfaction with the arrest of the city's mayor Ekrem Imamoglu - widely seen as President Recep Tayyip Erdogan's main challenger - for alleged corruption.
AFP welcomes Thursday's acquittal, but rejects the case itself.
Journalists must be allowed to cover demonstrations and protests unhindered, says the news agency's global news director Phil Chetwynd.
Swede Joakim Medin was also arrested in connection with the March protests. He was released from Turkish prison on May 16, but remains charged with terrorist crimes, which will be tried in Turkey in Medin's absence.
