why photos imported from iPad are often rotated ??

I often take photos with my iPad but it always looks fine on the mobie device. Once imported to PC, it also looks fine.

However, after I delete the EXIF from the photos with tools like ExifPurge. A lot of the photos are rotated somehow, 90 degree usually. I just don't quite understand.

Yes I can rotate the photos back but I am really wondering why does that happen and how can the problems be solved?
i.e. A picture is not rotated after EXIF is removed.

 

That's because EXIF contains information on photograph's orientation and good applications use it to present the photo properly.
For example in IrfanView options there is "auto-rotate image on EXIF info (if available)".

If it's checked the photo is right way up based on EXIF, if it's unchecked (which corresponds to you removing EXIF info) there is no way for a program to know which way is up, so to speak.

 

In fact, the photos are NOT rotated after they 're imported, only if I delete their EXIF, they get rotated.

However, I pretty sure when I took the photo with my camera the orientation was correct and the photos displaying on my iPad is also correct. Why it remembers an incorrect orientation?

 

I don't think you understand me. The photos are rotated automatically as long as there is EXIF data available - that's why you see them correctly even if you make a photo while holding the iPad vertically. If it wasn't for EXIF data vertical photos would be horizontal (rotated by 90 deg).

 

But why as I bulk delete the EXIF all of the images with the EXIF removal tool.

When most of the images are rotated to an incorrect orientation, there are still a few of those images which are not rotated and still stays in the same (correct) orientation?
Why it's that?

 

Apple has a universal answer to that. You were holding it wrong (most of the time).

 

but why All photos are displayed in the correct orientation in the iPad? their orientation changes only when transffered to PC

 

I have run into this as well...all front-facing photos from my iPad are upside-down when I copy them into a Windows PC, even though they appear upright on the iPad.

My own uncharitable theory is that they're intentionally making the PC experience bad to fuel Mac sales. It's also the only way I can explain the train wreck that is iTunes for Windows.

 

As much as tin-foil-hat-theory does it sound, I kinda have to agree there.
iTunes is such a turd on Windows. Its performance sucked back when I had a single core P4 3 GHz PC, it sucked on this i7 720QM I'm currently typing from, and it would probably suck on an 3,5 GHz i5 I have back at home...