How can I line up multiple pictures with each other?

You can use Picaboo's Alignment Guides to make sure your photos line up perfectly. In Edit mode, when you drag your photos on the page you'll see a set of vertical and horizontal guides appear when you're lined up with another object on that page. Your photo will snap into alignment automatically. If you prefer to disable this feature, you can choose "Disable Alignment Guides" from the View menu. The View menu can be found by clicking on the More Button at the top of the program.

< More information on Alignment Guides