Z-machine XZIP Picture Library
Z-machine XZIP Picture Library is a unofficial name of a file format which was apparently never used.
The only known example of this file format (from a collection of Infocom source code) is called
This file stores multiple monochrome pictures, each of which is indexed by number and a DOS file name; they are numbered consecutively but the header can specify the first picture number. The pictures are then stored similar to Netpbm format 4, but with alignment with two bytes instead of one byte.
Apparently, there is also a variant which lacks the DOS file names and has all pictures the same size, for use as custom fonts for displaying text, but no known files of this variant format exist. (Despite the name, the previously mentioned file does not use this format.)
(No other implementation is known to exist.)