A jpg file is only a raster image. There’s no vector information in it from which to create edges. There are a couple of extensions that you might use. The first is TIG’s Image Trimmer. It requires a PNG image with transparent pixels instead of a white background. The extension is available from Sketchucation. Another one is BMP Tracer which requires a bmp file. See this post. In both cases you may find that the resulting geometry has been simplified more than you want or is rougher due to pixelation in your original image. But you can give them a try.