licensing is simply require the candidates understand the all basic of his craftsmanship and be competent to do his job without any supervision, able to deliver satisfactory results to his customers consistantly, they may have to take some training or mentorship before they are given a credential.
one very good example here is get qualifications from Master Photographers Association.
although it is not compulsory for photographers to get certified, nor customers must hire a certified photographer.
but the certified photographers will earn the recognition and respects from fellow photographers and customers.
and for the customers will know they are not hiring "an uncle Bob trying to make extra pocket money during weekends for buying some L lenses" to shoot their "Once In A Life Time Event"