Vectric makes a line of popular software products. Here is one example of a workflow to create a G-Code file using these applications.
Of especial interest is Design and Make, available from: http://www.designandmake.com/ — AIUI, this application / web site was originally a 3rd party, but was purchased by Vectric. The software “Design and Make Machinist” is freely available, and will allow one to use free and purchased clipart, adjusting and repositioning it as desired, then export it into a form which may be imported into other Vectric products. EDIT: Note that such files may also be exported as G-Code as noted below.
Download, install, and launch Design and Make Machinist: