TilePic is a file format, and associated software, developed by the Berkeley Digital Library Project. It is a relatively simple container format for tiled graphics. The tiles can have arbitrary image formats. There is apparently a portable way to use it with JPEG format.
The format (or a profile of it) is sometimes called Tiled JPEG File.
Files begin with bytes
'T' 'P' 'C' 0x0a.
- tilepic file format man page (from archive.org)
The original TilePic software is open source, but we have not been able to locate a copy of it. It was once available at ftp://elib.cs.berkeley.edu/pub/gis/tilepic.tar.gz.
- Archive of TilePic website
- TilePic: a file format for tiled hierarchical data - ResearchGate page about a paper about the format