We look at images every day, but we rarely think about how they are built. When you see a product photo on a shopping website, it usually floats perfectly on a clean white space. When you see a logo on a website header, it sits neatly on top of a colored bar without a clumsy white box around it. This visual magic happens through a process called background removal. To the human eye, it is obvious where a person ends and a wall begins. But to a computer, a photograph is just a flat grid of colored dots. Teaching a computer to separate the "subject" (the important part) from the "background" (the noise) is one of the most difficult challenges in digital imaging. In this comprehensive guide, we will explore exactly how this technology works. We will explain the science of transparency, why some images are easy to cut out while others are impossible, and the crucial file formats you must use to save your work. Whether you are selling products online or just making digit...