The main hall of a temple, which was the origin of butsudan, represents Jodo (the Buddhist pure land) and, therefore, no picture of the dead is decorated inside its sanctum, and accordingly no picture is put into butsudan.
仏壇のもととなった寺院の本堂は浄土を表したものあり、内陣も故人の写真を飾っておらず、仏壇もそれに倣い飾らない。