There is however, two dimensions to this idea. The first is the subject's matter, the concrete, recognizable elements in the photograph. The second is the subject's theme, the way the photographer has interpreted the matter. It is, in fact, this latter dimension that creates the stylistic differences between artists and which can also be called their personal expression of the subject. Without this expressive element you are just making photographic records.
Unlike painting, where the artist can manipulate color and brush stroke to create an expressive interpretation of their subject, a photographer has to find this expression in something within and inherent in the subject's matter itself.
Studying the Visual Elements (line, shape, color, value, texture and space) and the Principles of Design (balance, unity, contrast, pattern, emphasis, movement) is imperative for photographers who want to create more expressive images.
There are many, many books available to the aspiring photographer to study these ideas but two excellent ones are by Michael Freeman, The Photographer's Eye and The Photographer's Mind. What makes these books good, in my thinking, is that they don't deal with the mechanics of digital photography like white balance, various settings and exposures but with compositional considerations...how accomplished photographers compose their images and, more importantly, why they do it that way.
As for the photographer's heart, that book, as such, has not been written to my knowledge. I would recommend Christine Valters Paintner's book Eye of the Heart for the time being. Ultimately, this third approach is the most critical for the contemplative photographer. What does your heart tell you as you walk around a landscape? Why do you point your camera's lens this way or that? For now, you must answer these questions for yourself...it is an intimate and personal consideration.
In later posts I'll discuss some specific subject matters that have been long associated with photography and the contemplative's approach to these subject matters. For now, I've added a link to a short video of one photographer's walk around a carnival. Study the video, pause it from time to time to see the "stills" and ask yourself what this video says about the photographer through their choices...an interesting exercise.