You should have a paper (in the country-specific guide) that states specifically what is required. It's the last page in the PDF for the USA.
It (at least in the USA guide) states:
The back of one (1) photograph must:
bear the name and complete address of the photography studio;
bear the date the photograph was taken;
The photographer may use a stamp or handwrite this information. Stick-on labels are unacceptable
What is required at the back of ONE of the photographs as per the regional guides is:
-date, name and address of the photography studio.
This info can be stamped or handwritten.