Why phone photos look sideways and how rotation fixes them
The EXIF orientation flag, why some apps ignore it, and how a real pixel rotation permanently fixes a sideways photo for every viewer.
The camera did not turn the pixels
When you hold a phone sideways to shoot, the sensor still records the scene in its native landscape layout. Rather than rewriting every pixel, the camera stores a small EXIF orientation tag that says how the image should be turned for display. The pixel grid on disk is unchanged; only a hint travels alongside it. This is fast and saves the phone from reprocessing a large photo, but it pushes the work of turning the image onto whatever program opens it later.
Why the same photo looks right in one app and sideways in another
Modern photo galleries and browsers read the EXIF orientation tag and quietly rotate the picture as they draw it. Older software, some email clients, and many upload forms ignore the tag entirely and show the raw landscape pixels, which is why a portrait suddenly appears on its side. Because the tag is only a suggestion, you cannot rely on every viewer honoring it. The safest fix is to bake the rotation into the pixels so no interpretation is needed.
How a real rotation makes the fix permanent
This tool does not just flip an orientation flag. When you press Left 90 or Right 90, it draws the decoded image onto a fresh canvas that is physically turned, so the pixels themselves are rearranged. For a quarter turn the width and height swap, which is why a 4000 by 3000 photo becomes 3000 by 4000. The exported file carries the corrected pixels with no orientation tag to misread, so it looks upright in every app, on every device.
Choosing a format after you rotate
A 90, 180, or 270 degree turn only moves pixels, so exporting to PNG keeps the image mathematically identical to the source, just reoriented. If you rotate by an arbitrary angle to straighten a horizon, the pixels are resampled and the newly exposed corners appear; PNG and WebP keep those corners transparent while JPEG fills them white. Pick PNG when you want a lossless result, or JPEG and WebP when a smaller file matters more than perfect fidelity.