Complex sentence: The photographic archive of "Picture Post" became an important historical documentary resource, and was set up by Hulton as a semi-independent operation officially incorporated as the Hulton Press Library in 1947.
Split into simpler sentences: The photographic archive of "Picture Post" became an important historical documentary resource. It was set up by Hulton as a semi-independent operation, officially incorporated as the Hulton Press Library in 1947.