What constitutes a perfect photo?
A decisive factor for a good photo is the resolution. Images for laser engraving should generally have a resolution of at least 300dpi as the output size. If necessary, you can increase the resolution in your graphics software by re-establishing the bitmap (example in CorelDraw under “Bitmaps” - “Resample”). For example, Internet photos often have a resolution of 72 dpi. Even these can be processed well with the laser, if the original images are large and are scaled down to workpiece size. You should avoid enlarging small images as this decreases the resolution (image raster becomes too large) and is therefore not a basis for a beautiful photo engraving.
Here's an example of a well suited vs an ill-suited image for photo engraving
The left image is well-suited for processing through the laser. It shows a good contrast, it is well exposed and the elements in the image stand out.
The right image is less suited for processing with the laser. Although the people stand out from the background, the exposure is too weak which makes the people look like they are in the shadows. This makes it difficult for details to be perceived and will result in the people being engraved as a unitary surface.