I purchased my tiles from ReStore for 8 cents a piece almost a year ago (yes, they have been patiently waiting). They are roughly 4" x 4" white tiles, they are not perfectly smooth on the edges but you won't know the difference once you have your picture/paper on them. I purchased exactly what The Cottage Home used except the spray sealer (Michael's didn't have that specific type) since I have tried other projects with "similar" stuff and it fail because the product wasn't as good. The one I did purchase did read "clear" and "sealer" on it so I figured I was safe. I will warn you that the clear sealer spray and the Fabri-tac were on the pricier side so use a coupon to make it better on the wallet. There will be plenty of Mod podge and Frabri-tac left over to make several projects. My friend and I actually made these together and we hardly put a dent in the Fabri-tac and about 1/3 of the Mod podge.
In case you are wondering about the photos I chose...
From top left to bottom right; Banana Cabana at the Isle of Palms, T and I at a NCSU tailgate in 2011, Katie and I having a beer staring out at the ocean, one of our engagement photos, and The Windjammer bar at the Isle of Palms.
Tips: Be very careful when applying the Mod podge because if you have lines... they will show up when they dry. I thought that the sealer might cover it, but I was wrong. The lines can't be seen unless you pick the photo up and look at the coasters. I would also get the felt as close to the edge of the tile as you can so when guests move the tile it doesn't scratch your furniture.
I think these make great coasters, I sat my coffee cup, wine, and water cups on them and they seem to work well. I was worried about the corners pealing up but that hasn't happened in about two weeks and we've used them several times.
This would be a great project to make as Christmas presents!!