This answer to Are there any photos of the Martian terminator from low Mars orbit? includes (without credit) what looks like an oft-repeated photo of Mars. A comment written from reverse image searching suggests it's from Viking-1 in 1976.
National Geographic says this is a Viking image and Universe Today says "…taken by the Viking 1 orbiter in June 1976." Forbes says "Image credit: NASA/Viking 1". While this is not really an image of the terminator, it's getting close; at the bottom right we see that the sides of tall features facing us are dark.
Since it's taken from orbit I've gone to https://photojournal.jpl.nasa.gov/Help/PIADetQuery.html and selected "Viking-1 orbiter" from the
Search for Images by Spacecraft option. The resulting search query https://photojournal.jpl.nasa.gov/spacecraft/Viking%2BOrbiter%2B1 yields thumbnails of 87 images which doesn't seem include this one. Then again 87 sounds low.
Question: Which Viking-1 orbiter photo is this? When was it taken and what part of Mars is shown?
With the time and identity of (at least some of) the features in the image known, I'd like to try to figure out the foreground's proximity to the terminator, possibly using the reconstructed trajectory in JPL's Horizons as well since it includes a model for coordinates on planets and their rotation.