First size and print you photos I did it in Picasa which is a free program and super easy to use.
If your wood piece has rounded corners trim your photo.
Glue your photo to the wood piece (I used both E6000 and mod podge on different occassions and they both work fine).
Punch a hole or if you don’t have anything to punch a hole you can just glue a ribbon loop to the back for hanging.
Next place your ornament on a flat surface and top with dimensional magic.
Pop and/or move any air bubbles you see off the edge.
Let dry (a few hours). It will appear cloudy at first but then it will dry clear.
String ribbon and hang on your tree.