What type of image is this?

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Well, openCV ist not so strong in reading raw image files. You should give a try to FreeImage, which is an open source library, especially for raw image loading and converting e.g. tone mapping.

Since it is a Canon camera, what is the file size of the images? If these are 15+ megabytes, it should be a raw image with ending ".CR2" or ".CRW". So, what do you mean with "renaming of some other program"?.

Try to make a copy of the image file and change it to ".CR2", for example. In FreeImage, which builds also upon LibRaw an image loading would be:

const std::string inpath = "input.cr2";  
const FREE_IMAGE_FORMAT infif = FreeImage_GetFIFFromFilename(inpath.c_str());

FIBITMAP* dib = FreeImage_Load(infif, inpath.c_str());

A conversion to openCV is normally possible. For testing purposes you could write this image to disk and see whats happening...