Imagine you want to draw a picture on a rock, but the rock is too hard to draw on with a pencil. So instead, you use a special tool called a chisel to carve your picture into the rock. This is what people did a long time ago, many many years ago.
The pictures they made on the rocks are called petroglyphs. Often, they would tell a story, like a comic book, but with pictures instead of words.
Now, what if you found one of these rocks with petroglyphs on them? You might not be able to tell what the petroglyphs mean. So what people do now, is they make a copy of the rock by using a special machine that takes pictures of the rock, and then makes a 3D copy of it.
This copy is called an image stone, and now you can study and learn from the petroglyphs without harming the original rock. It's like taking a photograph of a drawing, except this is a photograph of a rock with pictures carved into it.