Not every wedding, but many times when we are photographing the getting ready details, no one knows how to properly pin a boutonniere. When they try, a lot of times they end up crooked or falling off and looking for a lady to come and help!
A boutonniere should sit over the button hole on the left lapel of the wearer’s suit. You should not see any pins holding the boutonniere in place.
Here is a helpful diagram: