TOKYO >> A man suspected of sexually assaulting a woman figured out where she lived from a photo she posted on social media. In it, scenery of her surroundings was reflected in her eyes.

The Japanese public is being advised to take caution when posting pictures online, since smartphone cameras are capable of producing images of ever-higher resolution.

The 26-year-old suspect in the assault, arrested in September, allegedly waited for the woman and groped her body at the entrance to her condominium. When asked how he found the woman’s address, the suspect said he “got a clue” from a picture in which the scenery of the area was reflected in her eyes, investigators said.

Looking at the photo of her face, the man confirmed the reflection in her eyes matched scenery around a station. Then he used Google’s Street View service and other tools to find a station with similar surroundings, according to investigators.

The man allegedly waited for the woman at the station and followed her.

Reflections of such clarity are due in part to the eye’s surface, which is convex and reflective, said a professor of ophthamology. “The cornea on the surface of the eye is made from transparent collagen,” said Takashi Fujikado of Osaka University. “Scenery can be reflected in the eye, just like it can on the surface of glass.”

Since many Japanese people have black pupils and black irises, scenery can be reflected vividly. Young eyes produce reflections with the most clarity because their surface is smoother than aging eyes and more moist.

Another potential risk of today’s smartphone cameras: identity theft, stolen using fingerprints captured in an image. Japanese youth are especially vulnerable, since posing while making a “V” sign is popular among millennials there. Perpetrators can pass fingerprint authentication by reproducing the fingerprints from such an image.

V signs near the face are especially risky since fingerprints are more likely to be in focus.

Isao Echizen, acting director general of the National Institute of Informatics, encourages treading carefully.

“You should take some precautions when you post photos on social media, such as being careful how you take the images and intentionally reducing the resolution,” he said.