John Hope Muchirahondo is on trial in the High Court at Christchurch facing more than 30 charges, including rape and sexual violation.
Detective Brett Goucher told the court that thousands of images and a smaller number of videos were found on Muchirahondo's phone, and about 30 were deemed relevant to the inquiry.
Police had focused on the images that could be of sexual assault, he said.
Many of the images were of sexual acts, or naked women, with close-ups of genitals, and some of women being touched intimately.
The images were presented in a closed court room.
Goucher said they used some non-explicit images to confirm locations and the people in the images.
This morning, the High Court also heard from the owner of Chic bar in central Christchurch, Peivand Yazdanpanah, who said Muchirahondo had been a regular visitor to his bar over four or five years.
On one occasion he had said to Muchirahondo that he was very popular on the dance floor, and Muchirahondo had responded that he could have any woman.
Yazdanpanah asked Muchirahondo what he meant by that, and Muchirahondo pulled out his phone.
"It took a few seconds to scroll down to find the app," said Yazdanpanah. "Which to me was a bit odd, because you couldn't see any gallery [that] usually you see on the phone. And he said no this is my secret area. Then he put a pin code in, and opened the app and scrolled, and showed me the videos of having intercourse with other women."
Yazdanpanah said he was shown two clips of around 10 seconds, but could see files for about 20 to 25 videos.
He asked Muchirahondo if it was him in the videos and he said it was.
The trial continues.
