Some cameras and phones save orientation information in 'EXIF' tags. Most viewers can interpret these tags and display the images correctly, however, the image uploaded uploads the raw image data and this can cause it to appear 'side-ways'.

A work around at the moment is to use any image editor you have handy to rotate your image before uploading. 

For example is a simple online editor that can quickly perform this edit, along with other edits like resizing the image to improve your site load time.