Charges against Hasan were dropped by the Baquba criminal court because of insufficient evidence. He was accused of having ties to "terrorist" groups.
Military authorities had detained Hasan once before in Iraq before releasing him.
The second time he was arrested, his camera and videotapes were confiscated before he was sent to a military camp.
Aljazeera spokesman Jihad Ballut has said there was an ongoing trend in Iraq in which the Arabic satellite channel's staff were being targeted.
In October cameraman Samir Hamza was released by occupation forces in Baghdad after being held for two days. He was arrested while filming the aftermath of a bomb explosion outside a police station.
And correspondent Atwar Bahjat was arrested while covering a bomb attack in the al-Ghazzaliya district of the capital. She was detained in a US military holding area at Baghdad airport overnight, before being released.