file type error

I am tryind to open a image file that i took on a cannon digital camera when i got to the file on the computer it showes that there are images or data in the DMIS but when i open it the files that contain the images can not be read and insted show unassigend data type icon and under it it shows its a .CTG file. What i want to know is how can i open this type of file. do i need to download a converter and where can i find it.
Thank you for you help.