X-rays, traditional or digital, provide a 2D photo-like image. That is useful for examining much more than just bones. While it is used to highlight broken bones or liquid in joints, it also allows assessment of the internal structures, such as the size and shape of organs. X-rays are used to assess pathologies in the lungs like a mass, or to see the shape of the heart, the oesophagus, the trachea and much more. In the abdomen, it is useful to detect calculus in the bladder, in the kidneys, and even in the ureter. Your pet may have eaten something and now they are feeling under the weather? An X-ray will allow an assessment of the digestive tract and look for a foreign body.
Sometimes an X-ray is enough to make a diagnosis, but we have to keep in mind that it is a 2-dimensional image and organs are 3D structures. To prevent overlooking a condition, it is always better to take 2 X-rays, one perpendicular to the other, which allows us to visualize the third dimension. When we are looking for a thoracic tumour, for example, it is even better to take a third X-ray.
How do we get an image from taking an X-ray? The machine generates rays that cross the targeted area to reach a plate (which previously held a film like in photography) and transforms the data into images. Not all the rays reach the plate. Some structures with higher density don’t let the rays go through and appear white on the image (e.g., metal, bones, etc.), while low-density structures let the rays through easily (e.g., air, liquid, etc.) and will show as black on the image.