Can't open .CTG file from Casio Exilim camera on MacbookPro running 10.6.5 OS?
M0100.CTG is the name of the file. Tried downloading VLC free converter. It does not recognize the file type.

CTG files aren't meant to be opened and viewed. It is a compressed file containing info about all pictures on your camera. I think you should read the following link:

CLICK HERE TO READ INFO ABOUT CTG FILE EXTENSIONS (http://www.fileinfo.com/extension/ctg)

THIS IS AN OLD ASKMEHELPDESK THREAD PERTAINING TO THE SAME QUESTION (https://www.askmehelpdesk.com/advice/t-3727.html)

.CTG files contain image catalog information that is used by the camera when managing and displaying photos. You'll probably find a .ctg file for each set of images created.

The .CTG files should get deleted automatically when the associated images are erased, although it seems that current best practices are to format the memory card often so I wouldn't worry about the .CTG files.

If you've ever tried to open Mac files from a Jump/Flash/Key Drive on a PC, you've been presented with files that have a size of 0kb and are shaded when viewed. The files have an identically named file that is regular size in Kb. On a Mac these files are invisible but try to transfer them to a PC and they show up like a question mark.

The .CTG files are the same... they are usually invisible or just used like your house numbers... the .CTG files aren't the mail but they do tell the postman where to deliver or find your mailbox.