TLG is a raster image file format associated with the KiriKiri Adventure Game System. It appears to use a sophisticated compression algorithm.
TLG files may or may not start with a 15-byte "Structured Data Stream" header, of which the first 11 bytes are
"TLG0.0" 00 "sds" 1A.
Following that, or at the beginning of the file, is an 11-byte signature.
For TLG5, the signature is
"TLG5.0" 00 "raw" 1A.
For TLG6, the signature is
"TLG6.0" 00 "raw" 1A.
There are a few TLG files in the source distribution, e.g. kr2_224r3_src.tar.gz.