Comment by mjepson for I think that the problem may lie outside the OpenCV. OpenCV itself can't read jpg files (it is pretty complicate format), and thus it is using other libraries on your computer that can read jpg (I don't remember which ones). Maybe the problem is within those libraries. Or OpenCV failed to find appropriate dlls or something. You can put this theory to the test. Change format of your jpg files to pgm or ppm - very simple formats that simply store image buffer on disk without any compression (pgm is 1 channel image, and ppm is 3 channel image). I think OpenCV reading them without using any third party libraries. Check if your release build can read images in this format.

$