So, my guess is you are going to engrave the picture and then you want to cut around the edges, right? To do that you need to create a vector line the exact size of the engraved rectangle. Do it in one of the vector drawing apps like Inkscape (free), Affinity Designer (reasonable), or Illustrator (expensive). Let’s say you are using the free Inkscape. You will create a rectangle the size you want the finished piece to be, then you will place the artwork on top of it (resizing to fit if necessary), then save the result as an SVG file. Make sure your vector program embeds the JPG. I can’t be real specific about the commands since I don’t use Inkscape, but you can get a good start by trying the tutorials for Inkscape here.
Edit: one other thing. I’m not sure of the source of your image, but you will get better results if you can get your images in PNG format instead of JPG. JPG images can give lower quality results due to the introduction of image artifiacts.