I bought 4x4 sandstone tiles at a local home store. They were less than $4 for a square foot, which of course, is 9 tiles.
I added these cute felt stickies on the underside. I did add a drop of glue just to make sure they stayed
I found pictures I liked on line and did a screen shot, trimmed them to the size I wanted then reversed the picture. I printed them up on my printer on plain paper--don't use picture paper, it won't work. There are many free apps you can use to do this.
Now, I painted the top of the tile with Modge Podge and put the picture face down on the tile.
Let this dry completely. I usually let it sit overnight, but you can put it under a fan for an hour or so.
Once dry, put the whole tile under running water and soak it well.
Then gently start rubbing with your finger. The paper will rub off and leave the print on the tile.
Once it looks acceptable, allow it to dry, then brush on a clear glaze/protectant.
And here's the finished product. Suitable for use as coasters or to use as decoration!