When you upload an image to the site, sometimes the orientation is wrong even though it is fine when viewing the photo outside of the site. This is due to tags that some cameras add to the photos.
What is happening is that advanced cameras like on phones and most DSLRs use a tagging system to orient the photo (vertical or horizontal) which is then read by various other programs for photos. These programs range from photo editing software to basic photo albums on computers phones and social media applications.
However, during the process of adding them to the website, these tags can get stripped. This stripping of the tags can happen from any number of places including but not limited the computer’s operating system, the browser, various proxies on your ISP, etc.. The stripping, though, makes the photo not have such tags, causing then photos to default to a regular horizontal (or landscape) position.
The fix for this is the following:
Open the photo in any image program. This can be a photo editor like Photoshop or the default photo software on your computer (Ie: Preview in Mac).
Save (or re-save ("save-as" option)) the image (a different name preferably).
Use the re-saved image as the upload.
What this does is change the defaults of the image to the correct orientation without the need for tagging.