You can easy import pictures in JPEG or PNG format directly to SketchUp with using the import function. What jpg to skp conversion essentially does, is to place the image as 2D in a 3D environment, for example as a texture for one side a of a cube. Once this is done you can save the file in SKP format. It is not actual conversion, more of importing data.
Open JPG file Open SKP fileA 3D CAD translation software