You can enable readers to temporarily maximize the view of images, shapes, tables, charts, and text boxes in the completed book.
Select a floating or anchored image, shape, table, chart, or text box.
Note: To enable an inline object in a portrait or landscape template to be viewed larger, change the inline object to a floating or anchored object.
If the Widget inspector isn’t open, click the Inspector button 
in the toolbar, click the Widget inspector button 
, and click Interaction.
To set the object to be viewed full-screen when readers tap or click it, select the “Goes full-screen” checkbox.
To display the object as a thumbnail image that maximizes when readers tap or click it, select the “Uses thumbnail on page” checkbox (in portrait or landscape templates), then do either or both of the following:
Continue to edit the object: Select the thumbnail image, click Edit Frame, make your changes, and click Done.
Change the thumbnail image: Drag a new image to the thumbnail.