Last night I took a free class in Aikido (a Japanese martial art). All the students and instructor start off class by bowing down in front of a picture of the grand master who passed away about seventy years ago. Then they bow to each other. I was told by the Aikido instructor they bow to show respect for the deceased grand master and for each other.
I would like to know if it is a sin to bow down in front of a picture of a deceased human instructor to show respect?