Mystery. How do you capture mystery? Not all images need this to be part of their story but some do.
I have found that discarding colour can help focus the attention on what might be there, by way of lines and textures seen more prominently in black and white.
Less is more. Leaving out faces is a powerful way of conveying mystery. It leaves room to imagine and it also leaves room for the story to become part of the viewer's. We must be careful how we do this so the image isn't only an image without a face.
Here are two examples where I think mystery is found. In both images, the lines and textures, shadows and shapes all point to what is not there, but in a way that it is not missing. In the first image, we see some of the face in the shadows, just enough to speak of age and perhaps mood as well. In the second, we see none of the face but we see the earring and that is enough to open the door to imagine more.
Allowing the viewer to search for clues within the image and then piece the story together in their minds, colored by their own experiences makes room for a larger, ever expanding composition. The mystery grows for the photographer when the image begins to include more experiences and possibilities in what becomes a collaborative work with the patrons.
In writing, there is a saying that I think of often - Show, don't tell. In photography, it is also true in some cases. Like I said earlier, less is more.