If this image was featured in an article about photography, the alt-text could be something along the lines of:
“Close up, greyscale photograph of man outside, face in focus, unfocused background.”
If the image is on a website about a TV-series, an appropriate alt-text could be completely different:
“Star of the show, Adam Lee, looking strained outside in the rain.”
So write an alt-text that is as meaningful as possible for the user in the context they’re in.
Reading the previous section, you might be thinking to yourself: “I, as a sighted user, can see many details in the image, like who it is, how it’s photographed, type of jacket, approximate age of the guy and more. Why not write a detailed, long alt-text so a user with visual impairment gets as much information as I do?”
... read the whole story at axesslab.com.