In 1992, the Joint Photographic Experts Group (JPEG) finalized and released the JPEG file format. Most notably, the JPEG format uses lossy compression to greatly reduce an image's file size with little loss in image quality. This makes it easy for users to store several hundred or thousand JPEGs, transfer them between devices, and share them via email and the internet.

Due to its utility, JPEG has become by far the most common digital image format. Many digital cameras and image editing programs save photos, drawings, and graphics as JPG files, and most every modern PC and smartphone includes a default image viewer that can open JPG files.

There is no difference between JPG and JPEG files. Both are images saved in the JPEG format. The reason many JPEG files use the .jpg extension is that early versions of Windows limited file extensions to three or fewer characters. Thus, JPEG images saved in Windows could not use the .jpeg extension, and they used .jpg instead.

Since Windows became the most popular PC operating system, .jpg became JPEG images' default extension. That's why, even now, JPG files are more common than JPEG files.

In most cases and for most users, saving an image as a JPG file is a good choice. While JPEG compression does slightly reduce an image's quality, the dip in quality is usually unnoticeable to the human eye. Additionally, many devices and programs that save JPGs allow you to adjust the image's compression and quality level, to fine-tune its file size and appearance.

However, there are times you should not save an image as a JPG file. For example, JPG images are typically not high-quality enough for use on printed banners, brochures, books, and magazines. In these cases, you may want to save your image as a .TIFF file. Also, the JPEG format does not support transparency and does not do well at retaining the edges of sharp-edged text or graphics. In these cases, you may want to save your image as a .PNG file.