Bob's issue 385 from sourceforge http://sourceforge.net/p/filteredpush/tickets/385/

If a DwC-A has both occurrence.txt and occurrence_images.txt, then org.gbif.dwc.text.ArchiveFactory.openArchive(File unzippedFolderLocation) throws an UnsupportedArchiveException with comment "The archive given is a folder with more or less than 1 data files having a txt or csv suffix".

It appears that the more recent package https://github.com/gbif/dwca-io suffers the same fate. Not certain because using dwca-io I gave up trying to resolve a java compilation error in org.filteredpush.akka.actors.io.DwCaReader.

I was motivated to use zipped archives because I thought I understood Paul to say that some oddities about record ids become moot in that case.

Probably there are many archives with both occurence data and occurrence_images data, end ever more so in the future.