I take it upon myself to help out with these cases from time to time, and I'd like to show you what I've done. I don't really know why the forum software rotates images, but I think it has to do with image size. So here's what have I done.
1). I cropped the image. I cut out the edges which showed something other than the page. That takes up space, and isn't need for the purpose an image is posted -- to solve a problem.
2). I reduced the colors. The image was carefully storing all the varying shades of manila this paper had, and again, we don't need that information.
3). I resized it. It doesn't need to be 3264x2448, its going to be resized by the forum software anyway. I picked a reasonable size for the page.
And there you have it, a black and white image, centered on the page, ready to be worked with.
Did you notice, it just flashed onto the screen, the original has to build -- usually in seconds with decent bandwidth, but still.
This is becoming more of a problem, now that people are using cell phone photos and not scanners. Still, if you depend on the image to get stuff done, you may want to put a bit of effort on the message.