JPG and JPEG are exactly the same image formats. There is absolutely no difference between a .jpg image and a .jpeg image — they both use exactly the same JPEG compression algorithm and store image data in the identical manner.
The sole distinction is purely in the extension, as it is a historical artifact from early computer history. JPEG was introduced in 1992 by the Joint Photographic Experts Group. Early Windows launched early versions of Windows, the system enforced a limitation: file extensions could only be 3 characters.
This forced the 4-character .jpeg suffix to be reduced here to .jpg for Windows computers. Non-Windows systems, not having the extension limitation, continued using the longer .jpeg file extension from the start.
Although both extensions work identically in virtually all today's programs, certain cases where a platform requires the .jpeg file type. For these situations, changing the extension from .jpg to .jpeg is enough.
No real conversion of image data is necessary — just renaming the extension solves the problem almost always.
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