Why Is My Photo Sideways? How to Fix It
A picture looks perfect on your phone, then shows up sideways on a website, in an editor or on a print order. Nothing is wrong with the picture: it is a tiny label that gets ignored.
The short answer
Your phone saves the photo in the shape its sensor captured it, and adds a small note saying which way is up. Programs that read the note show the photo upright. Programs that ignore it show it sideways. Saving a copy with the pixels really rotated fixes it everywhere.
What is EXIF orientation?
EXIF is the information stored inside a photo: the camera model, the date, sometimes the location, and an Orientation value from 1 to 8. The value says whether the picture should be shown as is, rotated by 90 or 180 degrees, or mirrored.
Modern phone apps, browsers and operating systems apply it automatically. Older software, some upload forms, print services and several image editors do not, so the same file looks different depending on where you open it.
How to fix a sideways photo
Open the picture in a rotate tool that works on the real pixels, turn it the way you want, and save a new file. Because the pixels themselves are rotated, it looks correct in every program, whether or not it reads the orientation note.
If you need to mirror the picture as well, for example a selfie that was saved flipped, use a flip tool on the same file.
How to avoid it next time
Rotating and saving a copy before you upload or print is the most reliable habit. Sharing as a screenshot also works but lowers the quality. Converting HEIC photos to JPG with a tool that applies the orientation, like this site, gives you an upright file as a bonus.