Baca told Fox 5 he snapped the image outside the Georgetown AMC movie theater.
Biden was reportedly at the movies with his granddaughter, who was visiting him in town.
Biden has yet to publicly respond to the photo. A bystander took this candid shot. As of Monday morning, it had been shared more than 117,000 times and "liked" by more than 171,000 people. Facebook user David Laurence wrote, commenting on the photo. "It is always about family and in Joe Biden's world that means two things: there is nothing more important than family; and to Joe Biden, family includes every human being he encounters".
Biden was rumored to be eyeing a presidential run in 2020, Politico reported Friday, but he hasn't formally announced any plans to.
Biden declined to run for president in 2016, a decision he has since said he regents.
Biden is now on a book tour for his new novel about the loss of his son Beau, who died in May 2015 after being diagnosed with a malignant brain tumor.