Product images tend to rotate to landscape orientation instead of portrait orientation because the image doesn't fit the scaling requirements for your Timber site.
Your Timber site scales images instead of resizing them so the images keep their aspect-ratio, which keeps your images looking sharp and clean. If Timber resized the images it could cause the image to be distorted.
To get your images to all be portrait you should upload your image with the dimensions w150xh225.
If your images are uploaded as w150xh225 and are still displaying the incorrect orientation, please don't hesitate to send us an email so we can quickly resolve this issue.