I used a standard paintbrush, clear standard size tiles (bought individually at home depot for about $.13 a piece), a tool for pressing out bubbles, and Mod Podge (I used the hard finish type).
I coated the tile with a thin layer of the Mod Podge and also coated the back of a regular picture that I cut to fit the tile. For this project I used pictures of my mother-in-law's five grandchildren--one grandchild on each tile for a total of five coasters.
I used a tool like this one (it is actually a kitchen tool that I found that I have never used for food purposes) to flatten out the picture and make sure all the bubbles were gone from underneath the picture.
I then added a thin coat of the Mod Podge over the top of the picture. Don't worry--it dries clear. I allowed that layer to dry for about 20 minutes. I then put on an additional 4-5 thin coats of the Mod Podge to ensure the picture stayed and to ensure that the coating was hard enough so the coasters can really be used.
This is the finished product of one of the coasters. I added little sticker felt circles to bottom of the tile so that it wouldn't scratch surfaces (I forgot to take a picture of this step). You can also use cork cut to size and glued to the back with a spray adhesive. I stacked the coasters on top of one another and tied with a ribbon. They were a hit and she loved them! The coating is hard and thick yet clear and can be used as real coasters. I will definitely do this again for someone else or even for myself.