When a photo is uploaded to a video project, it can sometimes display sideways depending on the orientation of the photo file or the device that the photo was uploaded from. For example, HEIC image files which are usually uploaded from iPhone have a tendency to display sideways when uploaded.
Rotating Images
Images that are appearing sideways in your slides can easily be rotated using the rotation buttons on the image. On the slides page, hover over the photo that is displaying sideways and you will see the two rotation buttons (clockwise and counter-clockwise). Simply click the rotation buttons until the photo appears in the correct position.