Forgive me for not reading all the responses first (I will go back and do it) but I didn't want to be influenced on my thinking just yet and give a response of what I feel about the essence / subject of an image.
There is a difference between subject and essence. The subject is tangible, easily recognized. The essence (to me) is more about the feeling it evokes in the viewer.
Does a photo need both?
I can't actually answer that.
I believe you can have an excellent image, with a strong subject -- and no "soul".
And you can have an "Oh oops, out of focus, what the heck did I just shoot?" image, with such a strong essence to it, that defies logic.
I went to Australia many years ago, and a colleague took us to the Adelaide Museum of Art. There were many very good paintings. Some where worth a second look for me, and some weren't. (Eye of the Beholder.
) I am not an artsy person, I have no idea what I'm looking at. I don't know if it's a famous painter, nor do I care. I like what I like.
Then I walked into a room with a single, very large painting in it. It was a landscape, brown on brown, nothing special when you looked at the photograph of it in the catalog.
The real thing? I was transfixed. I stood there for over an hour, completely blown away. There was so much detail, so many things to discover, so many little specks of light and shadow... I completely understood why this was the first painting they ever bought.
It had soul.
The subject was (probably) the people in it, but the artist went beyond the subject and managed to draw me into this tranquil river scene, making me a part of it. The entire painting evokes a sense of peace that makes you feel rested.
I went home. I could not get that painting out of my head and regretted not taking a print with me - so much so, I asked an Australian colleague if he'd go down there to get me a copy.
He did. I had it framed, and they wanted to put this big, broad frame on it. Tried desperately to talk me into some flashy, stunning frame. "It'll set it off perfectly."
I balked. I opted for an inch wide, muted frame that echoed the colors of the painting. I wanted nothing to take away from the image.
When it was done, and I picked it up, the framer actually looked at it from across the room and said it was the right choice. That his suggestions would have overpowered the image.
It hung above my fireplace for 25 years. (It's in the loft in the UK now, as I have no way to get it here in one piece atm.)
Take Ansel Adams and his photographs of Yellowstone.
I have seen many shots of the same scenery. In color. In B&W. All stunning. All excellent images.
So far none have quite stuck with me the same way the Ansel Adams ones do. He didn't just capture the subject. He captured the majesty, the play of light and shadow. He drew me in and made me part of it. Made me feel something beyond "Wow, what a beautiful place."
So to me, essence, soul, is more important than the subject. I want a photo / image / painting to evoke a feeling in me. If it doesn't, it's forgettable.
So no, a photograph does not need a subject to be a good photograph.
But it does need soul to be memorable.
I think that's what makes the difference between a good photographer, who does everything right, and produces stunning work, and one you keep coming back to, because they capture more than just what the eye can see.
Does that make any sense?