Why do pictures appear sideways on digital frame?

Pictures may appear sideways on a digital frame due to incorrect orientation metadata embedded in the image file. Most cameras and smartphones use sensors to determine the orientation when a photo is taken, saving that information in the image's EXIF data. If the digital frame does not read or interpret this metadata correctly, it may display the image in the wrong orientation. Additionally, some frames may lack the capability to auto-rotate images based on this data.