Hundreds have flocked to a motorway underpass in the US city of Chicago to view a stain on a concrete wall many say is an image of the Virgin Mary.
An apparition of the Blessed Virgin or a salt stain?
Police have been patrolling the emergency turnoff area under the city's Kennedy Expressway, where the faithful have taken flowers and candles.
"We believe it's a miracle," a woman told the Associated Press agency. "We have faith and we can see her face."
But the authorities say the image is likely to be a stain caused by salt.
"We're treating this just like we treat any type of roadside memorial," AP quoted city spokesman Mike Claffey as saying.
"We have no plans to clean this site."
News of the image, discovered last week, spread slowly through Chicago's Roman Catholic community - until a local television station aired a story about it on Monday.
By late on Wednesday, the shrine had grown to dozens of candles and a blanket of flowers.
Eye of the beholder?
"This is the first time I've felt something so deep in my heart," worshipper Raven Leroux, 57, told AFP news agency.
"There's something in the air her energy is here."
But another onlooker quoted by AP, Victor Robles, said he was sceptical about the alleged resemblance with the Virgin Mary.
"I see just a concrete wall and an image that could happen anywhere," he said.
The Roman Catholic Archdiocese of Chicago says it has not received any requests to investigate.
People in many countries have been drawn to images believed to resemble the Virgin Mary.
In a highly publicised case last year, an old toasted cheese sandwich said to bear her image sold on the eBay auction website for $28,000.