What's the difference between the use of past participles as postpositive attributives and passive voice! A:What are on show in the museum B: Some pictures (draw / were draw) by the Africans

What's the difference between the use of past participles as postpositive attributives and passive voice! A:What are on show in the museum B: Some pictures (draw / were draw) by the Africans

Some pictures drawn by the Africans are on the show.drawn By the Africans is used to modify some pictures. If we add were, two verbs will appear, which is obviously wrong