If the image is too long, then click and hold (GRAB) the vertical
scroll bar on the right and drag it towards the bottom of the screen.
The contents of the window will scroll up, so that you may view the
entire image.

If the image is too wide, then click and hold (GRAB) the horizontal
scroll bar on the bottom of the screen and drag it to the right side
of the screen. The contents of the window will scroll from right to
left, so that you may view the entire image.