Why are some Buddhist scriptures and calligraphy pictures carried on your back?

Because those calligraphy pictures were copied from stone tablets.

Not all Buddhist scriptures are recorded in books. Many Buddhist scriptures are actually carved on stone tablets. In order to pursue realism, some experts directly carved Buddhist scriptures on stone tablets with paper, and the carved Buddhist scriptures were carried on their backs. This principle is the same as looking in the mirror.

Ancient artists in China integrated the artistic conception of Buddhism into China's architecture, sculpture, painting, craft, calligraphy and music, thus creating a more meaningful Taoist style.