The majority of the time that I upload a photo to wordpress (so I can insert it into a post), wordpress rotates the image 45 degrees. I've found that the only way to prevent this is to crop my photos in advance so that they are always "landscape," i.e. the width is greater than the length.
However, sometimes, I want to put a photo in a blog post that is taller than it is wide. Even when the photo appears upright when viewed in my mac's Finder, and when viewed in Photoshop, WP seems to disagree, and "corrects" it for me.
To date, I have not found a way to keep this from happening without cropping the photos to make wordpress happy. And I've had a very difficult time finding solutions for this, because searching for "image rotate wordpress" or similar invariably leads to a discussion about a "rotation" in the sense of exchanging one image for another, whereas this problem is about a single image being turned to appear at a different angle.