Navigating Image Documents
Click and drag an image to move the image inside its document window.
You can also click and drag the "red box" area in the thumbnail image in the top-right corner of the image document window, and the image display will move accordingly inside the document window.
You can also click to select any location on the thumbnail image to recenter the image display on the location of the image inside the document window:
Magnifying Image Documents
Click and drag the solid, circular scroll-grabber button on the vertical scroll bar on the left-side of the image document window to magnify the image display.
You can also click to select anywhere on the left-side scroll bar to jump to a specific magnification.
With the image document window selected, you can also use your trackpad to magnify and demagnify the image display.