I reported this to Melody and she wanted specifics and I went back thru my latest reading and found only two. I know Ive seen it more often than that. Let me know here and I will send to Melody.
Photos on their sides? post here
Most sideways pix are from straighttalk phones. If you do not go to the 'gallery' and then the pic, hit 'menu' 'more' and 'crop', then flare out the box that appears- you upload a sideways pic. Some folx lose trax of which pics they've edited to size, or just dont bother... they are mobile uploads.
From what I can tell there are some iOS systems that the auto rotate does not remain when you upload an image (not just on DG, but other places as well)
kittriana is correct. It is in the way your phone saves the image.