The Federal Government says footage shot by the Customs ship the Oceanic Viking, of Japanese whalers killing a whale and its calf, will strengthen any legal case against the whalers.

The footage, released by the Government today, shows a slaughtered minke whale and its calf being hauled up the ramp of the Japanese ship, the Yushin Maru.

The Government is extending the duration of its whaling surveillance program and says the Attorney-General is still considering what kind of legal action should be taken and who it should be brought against.

Federal Environment Minister Peter Garrett says the pictures released today support Australia's position.

"I think it's explicitly clear from these images that this is indiscriminate killing of whales, where you have a whale and its calf killed in this way," he said.

"To claim that this is in any way scientific is to continue the charade that surrounded this issue from day one.

"This is the indiscriminate killing of a whale and its calf. It's not scientific, and these pictures make crystal clear what's actually happening in the Southern Ocean, and make crystal clear why we so strongly oppose the activities of the Japanese whalers there.

"The power of the camera and the release of some of this footage means that not only Australians, who care deeply about the fate of these beautiful creatures, but people right around the world, will have a better sense of what's going on down there."

"These photographs show the reality of whaling, the reality of the slaughter of these animals," Customs Minister Bob Debus said.

"They will help us to back the Australian Government's argument in an international court case, the details of which are still being worked out."

Mr Debus said legal action could be taken in the International Whaling Commission or the International Court of Justice.