- 'works' is viewer dependent, to a degree.
- a photo only 'works' for a viewer if the viewer is engaged by it in some way.
- 'works' is frequently more then 'what a pretty flower' or similar.
Form and composition matter. If your photo captures the eye, you're a leg up on capturing the mind. There still has to be something in the image, though. If it's a busy mess with a deeply fascinating subtext, the eye will bounce off it before the mind senses the subtext. If it's a beautifully composed picture of a flower, the eyes will land on the flower, but the mind will wander away in a few moments.
An aggressive post-processing technique (e.g. HDR) may interest the eye, but if there's nothing in the image, the mind will wander away again. The eye rapidly tires of gimmicky effects, anyways. HDR will not save a rotten image.
An unusual angle may capture the mind and eye for a moment, begging the question "what is that?" but the answer had better be something worthwhile. If it's "my cat's nose" the mind justly feels cheated, and again, wanders off. If work is demanded of the viewer, there better be a payoff.
Portraits are generally good. People tend to find people's faces interesting -- the eye is engaged. A portrait also begs questions, "what is he thinking?" "who is she?" and so on.
What's interesting about your image? A picture of a flower that manages to evoke the feeling of springtime has 'worked' but one that is merely another pretty picture has not, really, or at any rate not as well. Does your image evoke a feeling? Does it illustrate a truth? Does it inspire a question? Great.
Most photos shot serve only as proof that the photographer was there, and they work only for the photographer evoking that moment in time all over again. These are called snapshots, and they don't work for anyone else, generally, in any useful way. They may, perhaps, make the viewer hate the photographer which is a reaction of sorts.