It’ll look correct in older applications. Change it in an old application that doesn’t understand the Orientation tag and the application will move the actual pixels around in the image, giving it a new rotation. Rotating the image doesn’t exactly help, either. Some programs–especially older image programs–will just load the image and ignore the Exif Orientation tag, displaying the image in its original, unrotated state. Newer programs that obey Exif tags will show the image with its correct rotation, so an image may appear to have different rotations in different applications. Unfortunately, not every piece of software obeys this Exif tag. The image data is saved in its original, unrotated form, but the Exif tag allows applications to correct it. In theory, then, you could open that photo with an application, it would look at the Exif tags, and then present the photo in the correct rotation to you. It adds this information to the Exif data that all photos have (which includes the model of camera you took it with, the orientation, and possibly even the GPS location where the photo was taken). So rather than performing the computationally intensive task of rotating the entire image, the camera would add a small piece of data to the file, noting which orientation the image should be in.
Digital camera hardware just couldn’t handle saving the image directly in rotated form. RELATED: What Is EXIF Data, and How Can I Remove It From My Photos? If you take an image in portrait mode, the camera knows and can act accordingly so you don’t have to rotate it yourself. The sensor detects which way you’re holding the camera, in an effort to rotate the photos properly. Manufacturers wanted to solve this annoyance, so they added rotation sensors to modern digital cameras and smartphones. The rotated image would appear the same in every program…as long as you took the time to manually rotate them all.