The spelling of these very special Tibetan objects varies greatly. Apart from the most common form "Zanpar" you will find other like "Zangpar", "Zenpar" or "zan-spar" and many more.
So far Zanpars have been neglected in Tibetan research. There are only a few publications mentioning these forms in passing.
Any closer research of the backgrounds, the meaning and the use of Zanpars is extremely difficult because any written classification of the use of Zanpars in Tibetan monasteries was not usual. Only oral legend existed which led - after the Chinese occupation of the country with the subsequent running down of the Tibetan culture - to present vagueness of this whole matter.
The basis of these exclusively oral legends was also found in the principles of some Tibetan teaching traditions which propagated just oral legends without any written records.
Very often the pre-Buddhist Bon religion is named as the origin of the Zanpars. But there are also other interpretations that refer as origin Iran or India. Even Greek, Jewish, Christian and Phoenician sources are sometimes mentioned. None of these speculations can be verified.
The basic idea of the Zanpar practice, i.e. to copy pictures on form by imprinting is surely true for most cultures & periods. So similar practices outside Tibet do not necessary serve as example. Therefore it is impossible to settle the question of origin definitely.