.jpeg and .jpg are the same image format — this tool re-encodes your file and saves it with the standard .jpg extension, which some upload forms and tools expect.
Nothing is uploaded.
JPEG and JPG are identical formats — the extension difference is historical (older Windows systems required 3-letter extensions).
Your image is drawn to a canvas and re-exported as a fresh, standard .jpg file.
Get a file that any tool expecting ".jpg" will accept without complaint.