When adding pictures to your presentation, you might want to add a picture larger than the slide size or maybe your picture does fit but you don't want to use the entire slide for its display.
For the above and many other examples, you can use the Image Scroll:
When clicking on the 'Image Scroll'-button, this pop-up will appear:
Where all you have to do is to fill in the 'Display Label' and select the relevant image via the 'Select File'-button.
After clicking on 'Create', you will see a red square with the selected image in it on the slide.
The size of the red square is the display window in your presentation. The part of the image that falls out of this square will be "scrollable" when you are presenting the slide.