Final answer:
To emphasize a subject or object in photography, the technique used is a shallow depth of field, achieved by using a wide-open aperture so that the subject is in focus and the background is blurry.
Step-by-step explanation:
The technique used to emphasize a certain subject or object in photography is shallow depth of field. This is achieved by using a wide-open aperture when taking a photograph. A shallow depth of field means that the area in focus is quite narrow, with the background and sometimes the foreground appearing blurry, thus drawing attention to the subject that is in sharp focus. Conversely, a large depth of field is obtained by using a closed-down aperture, which brings both the foreground and background into focus and is commonly used in landscape photography.
To create a 3D effect in a 2D image, you can employ a shallower depth of field, whereby the subject is in focus while other elements are not. This can effectively separate the subject from a distracting background and make it stand out as the focal point. Techniques like zooming in on the subject help to fill the frame and minimize distractions. By understanding and controlling the aperture settings, and consequently depth of field, photographers can direct the viewer's attention to the intended subject.