If the stones must be separate, you must draw them. It's clicking with the pen tool in Corel Draw or with point-to-point polygonal selection tool in a photo editor.
No need to be exact, but obey coarsely the stone edges because you will get plausible result. In a photo editor you can actually have the stones in one layer and paint to the cumulated selection into a new layer with the paint bucket after selecting around say ten stones.
With solid background it can seem quite plausible:
If you do not want so sharp stones, it's at least in Photoshop possible to refine the selection and there make it a little smoother:
If your photo editor is Paint Shop Pro, you have less tools, but it's freehand selection lasso seems to be excellent when one draws around the stones and the result need not to be pixel perfect. It makes plausible stones without smoothing. But there's also point-to-point clicking selection mode and selection smoothing tools.
It can be better to fill the areas as sharp and then select the emptiness around the stones with the magic wand, refine the edge and press DEL. Save also a layer copy with sharp edges.
You can trace the BW image in Corel Draw if you made it in photo editor. Tracing settings affect radically to the result.
Unfortunately I haven't current Corel Draw so I'm not aware how one makes stones smoother if they are polylines with sharp corners (=drawn by clicking only). In ancient Corel Draw there's only one corner at a time curve editing tools.