You might be searching for version 3.1 because you want a free or cheap solution. But let me convince you why you should skip the download hunt and look at (or the newer "Photograv Pro").
Works on Windows 7 or later and supports common file formats like JPEG, PNG, TIFF, and BMP. The Verdict: Pros & Cons Photograv 3.1 Download
PhotoGrav is a specialized image-processing tool designed specifically for laser engraving. Its sole purpose is to convert standard photographs (JPG, BMP, etc.) into "dithered" images (usually black and white halftones) that laser machines can engrave cleanly onto materials like wood, leather, granite, and acrylic. You might be searching for version 3