What is the difference between jpg and JPEG files?

JPG and JPEG both stand both for an image format proposed and supported by the Joint Photographic Experts Group. The two terms have the same meaning and are interchangeable.

Both JPEG and JPG are bitmap compression formats for picture and image files with compression ratios ranging from 10:1 to 20:1. In fact, JPG and JPEG file formats are identical.

Older DOS-based computers were designed to handle a maximum "3-character file extension" which is why JPG was attributed to compressed image files. Newer Operating systems allow for longer file extensions as evidenced by .html. Accordingly, the JPG file extension was upgraded to the JPEG file extension which is the true acronym for Joint Photographic Experts Group.