Kurt Sneddon said he accidentally left his backpack on the downtown "B" train.
The backpack contained the only copy of wedding photos he shot for a friend over the weekend.
He and the couple have been posting a flyer everywhere, hoping someone recognizes it.
"The one beautiful thing is that the people of the city have been beautiful, the ones that I've come across," Sneddon said. "People have called me, texted me, just given me well wishes and felt so bad for me and stuff. That has really touched me."
Sneddon said he simply got distracted when he left the backpack on the train.
A $2,000 reward is being offered if the photos are returned.