Who are they?
Mars. Yes, the makers of M&M offer these directly.
About the product:
M&M with your photo on them? It sounds crazy but that is what it is. The photo is printed on each M&M using black food coloring for an ink. You select the colors for your candy and the packaging. You may also print personalized text instead of a photo and have a batch combining both.
Prices vary by size of packaging / amount of candy. A 7oz bag containing your candy is $11.99. The company ships using 2nd day air to make sure you get it as fresh as possible. Turn around time is around 10 days.