Many phones and cameras don’t physically rotate the JPEG pixel data. Instead, they save the image in one orientation and add an EXIF orientation tag telling compatible software how to display it.

That’s why one program can show the photo as portrait while another shows the raw pixel dimensions as landscape or displays it rotated incorrectly. The files don’t usually have “two sets” of metadata—some apps simply honor the orientation tag, and others ignore it.

If you want consistent results everywhere, rotate the image losslessly and clear/reset the orientation metadata so the pixels themselves are stored the right way around. Tools such as jpegtran or jhead can do this without recompressing the JPEG. Example:

jhead -autrot *.jpg

That reads the orientation tag, rotates the image data as needed, and updates the file so even software that ignores EXIF orientation will display it correctly.