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. Where, exceptionally, photographs are submitted, they must be black and white, must be on sheets of A4 size, and must respect the minimum margins and admit of direct reproduction. Colour photographs are not accepted, nor are colour drawings. See also PCT Receiving Office Guidelines, Chapter VI, paragraph 146 (GL/RO 146).
PCT AG IP 5.159
Section F‑II, 5.3, in the Guidelines for Examination in the EPO applies mutatis mutandis.