Thank you for submitting your item for appraisal. This appears to be a 20th century stone rubbing after a copy of a copy of a stone stele after a mural by the Tang dynasty artist Wu Daozi 吳道子. The original stone monument depicting a Guanyin is currently on exhibit at the Beilin Museum. Stone rubbings were a way to reproduce highly regarded art by applying black ink to the stone, putting a large sheet of paper on the mural and by applying pressure to the paper rubbing off the ink and thus transferring it to the paper. Today stone rubbings have caused so much damage to the original murals that it is no more allowed in most places to make stone rubbings. The estimate is based on similar stone rubbings sold at auction. As always "asking prices" in the trade can be higher and can vary.