Alright buckle in... I think you guys pretty much nailed it
@Raoul-Duke and
@Slater
I had the same questions a while back and being a techie I gotta know... It sort of has to do with how computers read and can rotate (or re-arrange) pixels vs how modern "smart" phones and
some digital cameras see and 'categorize' its orientation. These cameras are equipped with sensors that can tell which orientation to take the photo in. BUT the really cool part (or annoying part atm) is it's ability to even store that rotation information within the picture/video format itself.
Exchangeable Image File Format (Exif) and how most applications and OS' are a bit behind with understand
all of it's contents. Windows 10 (and 8.1 I think) understand (mostly) how to read all EXIF information. Now it's up to the indivuals applications you use to carry the information a bit further.
To illustrate: Think of your Camera as a person handing you a form to bring to another person (your PC / Application / Website / Etc.) If that person on the other end can only understand half of the fields of the form (ya know 'cause their new at this job and there's always some long bulls*** history there of how they even landed the job and they don't really know what they're doing... but are friends with...)
anyways, it just can't go much further without using the rest of the info provided!
That's partly why there are applications for importing mass amounts of pics taken where it arranges them all for you beautifully and yep, they definitely know which way should be right side up. (if and ONLY if your choice of camera bothers to fill out the whole form in the first place). If you read deeper into it, it goes back again... to pixels, if you rotate an image on your computer (depending on the application) you are actually degrading some of the quality of the photo VS an app that reads EXIF properly and doesn't re-arrange pixels, it just knows which way the photo should actually face.
That's about as much as I know and can understand in my current state of mind lol...
hope I didn't geek out tooooo much!