pictures are being cropped. How can I change height to correct this?

I just uploaded a file to Smashwords, ( www.smashwords.com/books/view/706192 ) and when I download the pdf file, My pictures are being cropped. The text is shown full screen width, and limited to the height of the screen in Adobe Digital Editions. How can I adjust the height so that the picture will be shown full height? I also notice that some pictures seem to be pretty well centered, while others sit on the left edge of the page. Is there a reason for this, and how can I correct it in my Microsoft Word .DOC file?