四分律行事鈔資持記 3.690

3.690

四中。令密藏者，不生善故。令恭敬者，恐生慢故。今時有作涌壁，或畫佛首相，並宜藏之。

In the fourth [part]: commanding that it be kept hidden is because [otherwise] good would not arise. Commanding respect is for fear that arrogance might arise. Nowadays, some create relief walls or paint only the head of the Buddha; these should all be concealed.