To quote Wikipedia, "An ex post facto law (from the Latin for "from after the action") or retroactive law is a law that retroactively changes the legal consequences (or status) of actions committed or relationships that existed prior to the enactment of the law."
I'm adopting the Latin term to describe retroactive influence, specifically, an influence that affects the way you assess a photo that you have already taken.
Have you ever looked at a photo you once ignored and reassessed it in light of work you had appreciated elsewhere? That is what happened to me today. I was sorting through some Paris photos for a project and my eyes stopped when I came across the photo above, not because it was what I needed for the project but rather because it made me think about the following Saul Leiter photos I had been looking at the night before:
Not that my photo is as good as Leiter's or that it was inspired by him at the time I took it. Two immediate differences: 1. there is no human presence in my photo and 2. the tones in my photo are less warm and saturated. In Leiter's photos, the angle of the hand or of the head draws in the viewer's eye. The slight glimpse of humanity haunts the photos. It makes me wish someone had been sitting in that blue car when I took my photo.
But my point is that I might never have noticed my photo today (which, although it is no Leiter work of art, still really pleases my eye) had I not been admiring Leiter's work last night.
Last night I had been thinking how I would like to do some photos inspired by Leiter. Today, I realized that I already had—retroactively. And that, dear reader, is my tale of ex post facto influence.