By default, Screenbook Maker resizes the image in the main Screenbook folder to be no wider than 640 pixels. The copy in the high resolution folder is not resized, however, the width of the "low resolution" copy determines what width will be displayed in the browser.

In most cases 640 pixels is an ideal width. However, you can change this default width by changing the Max Image Width setting in the Bookshelf Options dialog.