At least 149 people were on board the ferry when it capsized 86km northeast of the Tongan capital of Nuku'alofa. Two bodies and 54 survivors have been found, while 93 people are presumed drowned after being trapped in the vessel.
The navy divers believe they have found its wreckage but poor weather is delaying deployment of the ROV to confirm the find.
Today the navy released an image of the ferry sitting hull down on the sea floor at a depth of 110m.
Lt Cdr McMillan told NZPA that when the ROV was deployed, it would show a high level of detail.
"The main aim of the mission is to formally identify the vessel -- find the name plate and read it," he said.
"In the course of that investigation, it is likely we will observe other things on and around the vessel.
"If there were bodies down there and they were in a near locality or on the vessel, then there is a chance that we will observe bodies."
All imagery would be given to the Tongan government, and it was up to it what it did with the footage.
The ROV was expected to be deployed once the weather cleared on Monday evening.
Navy dive ship HMNZS Manawanui was due to arrive in Tonga on Saturday, and the ROV would be deployed from it.
The vessel was lying in 110m of water -- 50-60m too deep for the navy divers to reach, Lt Cdr McMillan said.
"It's extremely frustrating for us," he said.
"We're sitting around waiting when we could be out there positively identifying the ship and giving the Tongan people some answer on that.
"We have established to a very high confidence level that it is the Princess Ashika -- I think there's no doubt that it is -- this will provide that formal finish."
The surveyor in charge of carrying out checks on the ferry said it was not seaworthy, but Tongan Transport Minister Paul Karalus has maintained it was.
He resigned on Tuesday but denied he was admitting responsibility.
He said he had resigned because his ministry was the subject of a Royal Commission of Inquiry.
Prime Minister Feleti Sevele has said the seaworthiness of the ferry will be investigated by a commission of inquiry, though he noted that he had himself seen the ferry's certificate of seaworthiness.
Meanwhile, deep sea recovery expert Bill Day said it was possible to recover bodies from a depth of 110m, but at a huge cost.
"That sort of stuff's done all day around the world, but you're talking about equipment that isn't in New Zealand and will have to be brought into Tonga," he said.
"It's hundreds of thousands of dollars a day to run an operation like that."
Mr Day said he believed the cost, the potential dangers for the divers and the months it would take to complete the recovery meant that it was unlikely to happen.
"Very sad as it is, this may be one that's impossible to do."
Police Commander Chris Kelley said the identities of 37 people among the missing had been confirmed, including four crewmen, six children, 13 women and 14 men passengers, The Associated Press reported.
Officials were still trying to reconcile conflicting details of the remaining 56 people believed to be aboard.
"The process will take some time. Realistically, it may never be 100 percent accurate," Kelley told reporters.
Police Chief Inspector Sokopeti To'ia said the problems in confirming the identities were due to some names on the manifest being shortened or only first names being used.
Also, some people bought their passage but never boarded the vessel, and in some cases "somebody else got on instead of them," she said.
