Institutions: includes the Rubens House, Plantin Moretus Museum (printing), Hendrik Conscience Heritage Library, MAS and more. Their online collections database is being constantly updated.
The interface is available on in Dutch at the moment. There are some guides to searching here: https://dams.antwerpen.be/api/lod-search
The images are available for download directly as low res JPEGs or high res TIFFs.
I can’t find any conditions on the website, but was told by Steven Van Impe of City of Antwerp museums that these images are free of copyright. Many thanks for this information.