Files with ctg extension can be typically found on memory cards of Canon digital cameras along with captured photos. Contains index and other information for faster loading of the pictures.
CTG file extension - Canon catalog index
What is ctg file? How to open ctg files?
File type specification:
File extension ctg seems to be best known for its use for so called catalog files generated by certain Canon digital cameras used since early 2000s.
You can usually find these files on memory cards for each picture set. These are used to provide additional information for viewing and managing of associated photographs.