I may be wrong but there's not as much that can be done accurately (relative word here) with a raster image like a jpg file. You can sometimes import an image and then trace the geometry over it for use but I've never used that method. I've heard that you can also use Illustrator Professional to create a vector image with but I've not used that either so perhaps somebody else more knowledgeable can chime in on that.
When I need to create something for machining, manual or CNC, I make a CAD model so I know what my geometry should be. As far as I know, anything that uses a raster image or an optical/laser derived dimensions is subject to a built in degree of inaccuracy, +/- .007 is about as good as it gets. For lots of work this is just fine, it just isn't close enough for what I do.
Sorry I couldn't be more help.