cover.graphic.file Ant parameter
Specifies the absolute or relative path of the graphic to use as the cover graphic for the EPUB.
An absolute, platform-specific filename or a path relative to the root map to a JPG, PNG, or GIF to use as the cover graphic.
"" (no cover graphic or cover graphic determined by markup in the input document).
coverGraphicUri (via Ant's conversion of filenames into URIs).
See Creating Cover Graphics and Covers for more information about EPUB-specific cover graphics and alternative ways of specifying the graphic to use.