JPG and JPEG are both popular image formats – and the only difference between them is the visible one. Older Windows versions did not allow for file extensions with more than three characters, hence why they used .jpg instead of .jpeg, which was commonly used on Mac and UNIX systems.
Even though Windows computers now also support files with the longer, .jpeg extension, the three-character extension has become more widely used. Other than the additional character in the file extension, there is no real difference between JPG and JPEG images.