Have you always wanted to carry your favorite first edition around with you all the time? Okay, well, that's probably not really possible, but you can make a necklace using a book cover image! You can also use this as a starting point to make ornaments, keychains, or coasters.
This tutorial assumes you have access to and general knowledge of how to use a laser cutter. If you don't, consider a service like a service like Ponoko (although I have not used them myself).
This will work best with a fairly simple cover, like the original Hound of the Baskervilles cover shown here.
For laser engraving, it's best if you can reduce the image to a simple black and white image. This is doable with free, open source editing software GIMP.
We're going to use thresholds to divide the image into black and white pixels. You may want to invert the colors first if you have a light color that you want to be the black pixels. To do so, go to Colors > Invert.
Now go to Colors > Threshold. Play around until you get the image such that the pixels you want are mostly black with not too much background noise.
And now for the tedious part: cleaning up all the background noise. I recommend using the pencil tool with a white color to overwrite the background noise and with black to fill in any holes that didn't make the threshold cutoff.
I also did a version where I did not invert first so I could capture the hound in the center. I cropped out the hound, copied to a new image with a transparent background, and erased some parts. Once I was done cleaning the first image, I copied this image onto the first one to get the hound on there. I drew some white space between the hound and the other features to make the distinction clear.