That differs from confession to confession.
Most of the time our Signora Paola uses her own screenshots. For other characters she takes them from other blogs like @madeinmasyaf !
I for my part google certain pictures (e.g. for a crossover I googled Tom Hardys face) or scan them like sketches from the artbooks I possess 🙂
Hope that helped!
-Sister Teodora.
(People take their screenshots on PC or via the screenshot mode from the current gen (PS4 and Xbox One))