Key facts
- MIME type image/jpeg; .jpg and .jpeg are the same format. Files start with FF D8 FF and end with FF D9.
- Lossy DCT compression with an adjustable quality level; no transparency support.
- Usually carries EXIF metadata: camera model, date, orientation and often GPS location.
- Typical photo size is 1-8 MB from phones and 50-300 KB for web-optimized images.
- Progressive JPEGs load blurry-to-sharp; baseline JPEGs load top-to-bottom.
How to open a .jpg file
Windows
Double-click to open in Photos; edit in Paint, Paint.NET, GIMP or Photoshop. Browsers open JPEGs too.
macOS
Opens in Preview, Photos and Quick Look. Use Tools > Adjust Size or File > Export with a lower quality to shrink it.
Linux
Use the default image viewer, GIMP or a browser. Inspect metadata with exiftool photo.jpg and losslessly optimize with jpegtran -optimize -copy none -outfile out.jpg photo.jpg.
Common problems and fixes
- Bottom of the photo is grey or the image is cut off
- The file is truncated, usually from an interrupted transfer or failing storage. Re-copy it from the original source; recovery tools can only rescue the part that was written.
- Photo shows sideways or upside down
- The camera stored rotation in the EXIF Orientation tag and the app ignores it. Rotate and re-save it, or use a tool that applies orientation before stripping metadata.
- JPG is too large for upload or email
- Resize to the needed dimensions and re-encode at quality 75-85, which is rarely visibly different. WebP or AVIF can be smaller still where supported.
- Photo reveals my location
- Phone photos often embed GPS coordinates in EXIF. Strip metadata before sharing; most social networks remove it, but email and file sharing usually do not.
- .jpg file will not open
- It may be an iPhone HEIC, a WebP or an HTML page renamed to .jpg. Check the real type with the file command or a hex viewer and convert or re-download it.
Often converted to or from: PNG, WebP, AVIF, PDF, HEIC