The TI.Image format is a type of image used in several places in the Nspire documents, such as Lua scripts.
From what we can see with the help of errors in the Lua interpreter, the image is in fact a "tiff" file, encrypted and/or compressed in an unusual way.
The format has a header specifying the total buffer length. The header is 19 decimal numbers long.
Example header : .\000\000\000\018\000\000\000\000\000\000\000\092\000\000\000\016\000\001\000