Any image you serve should have government issued age documentation (in its line of succession) in verification of that person being at least 18-years-of-age.

"in its line of succession" means the producer (maker) of the image -- in other words, from where you have gotten the sexually explicit images. You would need this to raise an "affirmative defense" to issuing any underage explicit images.

If "Suzy" uploads her naked pictures to your server -- you better have ID documentation from Suzy to prove she is of legal age.

(Not given as legal advice for compliance with U.S.C. 18 §2257)