Plucker files are generated from HTML files where possible and from Plain Text files elsewhere. If the source file is a Plain Text file, the program must guess at the structure of the text. Thus plucker files may contain formatting errors like verse lines run together or paragraphs wrongfully marked as headers etc. They are good enough for reading though.
The generated plucker files do not contain images.
You may also install the plucker distiller software and generate plucker files yourself. This gives you more options, like including images etc.