To ensure your background fits perfectly without stretching: Go to the tab. Select Slide Size > Custom Slide Size .
You can apply your scroll image so it stays fixed as a background: Right-click the slide margin and select . Choose Picture or texture fill . Under Picture source , click Insert to upload your scroll image.
For more creative layouts, you can download pre-made scrolling effect templates or follow video guides from PowerPoint University for advanced "unrolling" scroll animations. If you'd like, I can help you: for a truly interactive scroll bar.