To achieve a black background in your photographs, you can start by controlling the lighting in your scene. One way to do this is to use a strobe flash or continuous light source and increase the light output. You can also move the background further away from the light source and into a darker place. This will help to create a contrast between the subject and the background, making the subject stand out more.
Another way to achieve a black background is to use camera settings such as aperture and shutter speed. By manipulating how the light enters your camera, you can change the look and feel of your black background photos. In manual, aperture priority, or shutter priority mode, you can adjust the aperture value to narrow the lens and limit the light entering the camera. This will make the background darker and help to separate the subject from the background. You can also adjust the shutter speed to control the amount of light entering the camera. A slower shutter speed will allow more light in and a faster shutter speed will allow less light in.
Additionally, you can use AI background generators to remove the existing background and replace it with a black background. This can be done using apps on your smartphone or software on your computer. By using these tools, you can easily and quickly change the background to black, creating a professional and visually appealing result.