Your mind supplies the missing parts if enough of the significant features are visible. A simple example of this can be seen with this series of circles. As more and more of each is removed the circle still remains identifiable until more is missing than is present. This works with a simple geometric shape because you need only a few clues to remind you of the shape. More complex objects require more careful consideration as to what can and cannot be removed.
Closure is used extensively in art.
It is not so much the quantity, but rather the quality of the information that lets you read an image. A clever artist leaves some things for the viewers to supply when they look at an image. It is a little like when the singer at a concert gets the audience to sing along. You feel like part of the show. It is based on the idea that once you start looking in a particular direction you will continue looking in that direction until you see something significant.