It is impossible to make an embroidery design (such as .jef files for Janome machines) from a bitmap source (.jpg for example) with just some simple graphics editor, it requires a special tool for that. That is because embroidery files are special vector based images that also have special instructions for the stitching machine so it can be sewn on the piece of cloth.
Which means, you will either need a dedicated embroidery program with digitizing function to achieve direct jpg to jef conversion or some experienced graphics designer that might be able to create embroidery design from some image.