One thing you could try would be. Take the picture and put it inbetween 2 pieces of clear glass or one clear and one colored piece for the background. Then put glass foil all around the two pieces ensconcing the pic inbetween, burnish the foil down well so the cement will not seep into it. If you are pouring into a mosiac mold you need to put cretelease on the mold so it will come out easily. Then cut a piece of contact paper the size of the bottom of the mold. Put the picture up-side-down where you want it on the contact and any other glass or whatever you are planning to decorate with. Then pour the concrete mix into the stone, carefully so as not to move the contact and picture. When you unmold the stone, peel off the contact and clean off any concrete that needs to be smoothed off. Then you need to use a sealent like Liquid Gold from HD but wipe any off the glass so it won't leave a film.

I have made patio stones using the mosaic method and pictures. You glue the photo side down to a clear piece of glass a little larger than the photo. After it is completely dry (I use Weldbond Glue) it dries clear, glue the picture to the patio stone. It can then be decorated with name, dates and other information using small pieces of stained glass cut in thin pieces and shaped into the letters. After all the gluing is dry you must grout the entire surface using a sanded floor grout. This will make it water resistant. After the grout is almost dry wipe the surface with a damp sponge and then polish it with a dry rag. Good luck.

If you want it to last long-term, you might think about visiting a framing shop and asking to buy some UV-resistant glass. Most photos fade very easily in the sun.

Dirtyhands, I am so sorry for your loss.

I had a picture of my son installed under glass at his grave and it has faded terribly. I seem to remember a few threads over in Garden Accoutrements or Hypertufa that discussed sketching photos in cement for a permanent image. Try doing a search.

Also, visit the Grieving Forum at That Home Site when you have a chance. You will find kind and generous people there who understand.