How to get a stronger contrast during laser engraving on stone?
In order to achieve a stronger contrast, you can fill the engraving with synthetic resin or lacquer. Especially in the case of polished stones, the lacquer or the resin adheres particularly well to the engraved (and thus roughened) surface.
What must be taken into account when engraving photos?
As stones have an uneven surface, they are best suited for coarsely rasterized images (250–333 dpi). Very fine and detailed images may be difficult under certain circumstances, but this depends very much on the structure of the stone.