Vector drawings differ from photos in a way that instead of being a grid of pixels (colored points) they are geometrical formulas defining shapes and are constantly interpreted by the software to calculate their on-screen render on a page. Vector drawings are perfect for graphics that need to be used at several sizes, like logos. They are perfect for documents that need precise rendering such as maps. The trouble with photos is when they need to be resized, they lose their quality, especially when scaled up. So when it's possible (that is, when the graphic result is made up of shapes or lines with flat colors or simple gradients) we try to avoid them. Vector graphics cannot replace the photos because their rendering differs too much. The rule would be: use vector graphics where a photo is not needed.
There is no way to replace a photo by a vector drawing because their graphical qualities are different. Vector drawings are mostly done with simple shapes, flat colors...