The PCT Regulations are silent with regard to photographs. Nevertheless, they are allowed where what is to be shown (for instance, crystalline structures) cannot possibly be presented in a drawing. See GL/PCT‑EPO A‑V, 1.2, PCT AG I 5.159 and PCT Receiving Office Guidelines, Chapter VI, paragraph 146 (GL/RO 146).

Section F‑II, 5.3, in the Guidelines for Examination in the EPO applies mutatis mutandis.