LibreCAD doesn't have raster to vector conversion built in. You may try an external program for that. In my experiments I have got best results with Wintopo, they offer a free version, but Windows only. When you are looking for a different tool, be aware that you need center line tracing, not all tools offer this, you will then always get double lines, marking the line thickness.
Generally these tools in most cases do not work satisfyingly for CAD, results being jaggy, not exact, not properly aligned vertically and horizontally. In most cases it is better to use the image as an underlay and draw on the top.