If you have a Staples or Office Max close by pick up a package of white label paper. It comes in sheets the size of a regular sheet of paper and has a plastic backing on the back of the paper that you peal off to reveal the sticker. They also make it in clear if you are interested.
If you have a picture that you have in mind that you want to use on top of the sound board in a jpeg format here is what I do. Open the picture and then right click on the picture and then open Word and paste it into Word. Once you have it posted to Word you will see the box around the outside of the picture. Grab one of the CORNERS and move the mouse to shrink it to fit onto the sound board. Make sure you grab it by one of the corners so that the picture shrinks uniformly, if you grab it from the top or bottom middle and change the size the subject gets fat or skinny like the mirrors at the circus if you get me drift. Print the picture onto some plain white paper and then lay your glass sound board over the picture to see if it fits the sound board the way you like. Once you have it the size you like put the label material in and print it onto the label.
Once you have it printed cut it close to size and peal off just one of the strips on the back of the paper and hold it up to the light and center the picture on the glass. Start from where the plastic backing is on the back of the paper and work toward the edge of the glass and then work from the center side to side to work our all the air bubbles. Take off the next layer of backing and repeat until you have the picture on the glass. Once its on the glass take a good sharp razor blade and trim the excess from around the edge of the glass.
Hope this helps you out.