If it’s music: key and tempo. If it’s photography: tone and subject. In other words, the key and tempo of music = tone and subject of photography.
When I look at a photo that has a blue-ish cast and the subject is melancholy, it would be easy for me to write a song that is in a minor key and has a slow tempo.
The opposite is also true. If I saw a photo of waves crashing high on a bright sunny day it would be natural to feel uptempo and think of a song that’s in a “happy” major key.
So for those of you who are into fusion (combining photos with music) this can be a powerful merging of seeing and hearing. Here’s a graph to illustrate:
On a business trip to CA I had some time at the beach and captured this guy going out just as the sun was setting. The temperature was in the 40's and he ran down to the water and then started walking.