Is there any difference between jpg and jpeg for website images?

one gotcha though: on most linux hosts filenames are case sensitive, so photo.JPG and photo.jpg are different files. cameras love saving .JPG in capitals, then the image breaks because the page asks for .jpg. lowercase everything on upload.

None, it's the same format. The three-letter version exists because old Windows only allowed three-character extensions. What matters for speed is file size and dimensions, so compress them and serve WebP if your setup allows.