Raster images are pixel-based, making them ideal for detailed photographs but prone to blurriness when resized. They should be used on websites for complex visuals where detail is crucial. Vector images, on the other hand, are composed of paths and are scalable without losing quality, perfect for logos and simple graphics that need to maintain sharpness across different sizes. Vectors are best for elements that require frequent resizing or that need to display crisply at varying dimensions on a website, ensuring a professional appearance regardless of device or screen size.