Ok, i found the fastet workaround for iphone / ipad users who are too lazy to turn on their PCs (i.e. me):
The iphone stores the pictures correct orientation in EXIF data instead of within the file format. vBulletin ignores the EXIF data when uploading, hence why pictures that are auto-rotated on the iphone via its gyroscope show up flipped.
Here’s the workaround:
1) Open the picture in iOS.
2) Rotate the picture 90*. The picture should be flipped to its side now
3) Save the edit. (This step is important, if you just flip it 360* iOS recognizes that you flipped it 360* and won’t save the rotation into the file)
4) Now open the flipped image and rotate it another 3x (270*) to get i back into the correct orientation
5) Save, then upload.