A faultless image.
This phrase alludes to the idealized settings and composition of wedding photographs, in which every detail is managed to obtain a perfect result. The phrase was coined in the USA in the early 20th century; for example, this piece in the 'Savannah Social News' column of the Georgia newspaper The Atlanta Constitution, January 1909:
"Exquisite decoration made the setting for the wedding picture perfect, quantities of lovely flowers being used in the adornment of the four rooms."
The phrase didn't catch on at the time though and was rarely used again until the late 20th century.