Between 2009 and 2017, official White House photographers accumulated an archive of nearly 4 million photos of the Obama administration. On average, that’s a little less than a photo a minute.

One can imagine what surprising gems are hidden in such a crush of images. And for Amanda Lucidon, her new book Chasing Light: Michelle Obama Through the Lens of a White House Photographer is a chance to share some of those previously unpublished photos.

Lucidon took a break from her book tour to speak with National Geographic about her time in the White House—and how it started with a surprise call from White House photographer Pete Souza.

I was pretty sure [Souza] had the wrong number.