Here is a very rough outline of the steps (I have used the Beyond Bullet Points book for the example). First you will need Photoshop or some other photo editing software that allows you to distort selections and save them as PNG files.
(2) Open the book cover image in Photoshop.
(3) "Select All" and copy the entire image (but do not paste yet).
(4) Go to "Image" in the menu bar and select "Canvas size...". Here you will want to add about 10-20% (depending on the size) to the height and width of the canvas to give you room to distort the image.
(5) Now that the canvas is bigger, "Paste" the original book cover image (it is still in memory or "clipboard" remember).
(6) You now have two layers. Next, remove the bottom later (you can just drag it to the trash can icon in Photoshop). You now see your book cover image with a checkered board canvas around it. This will allow you to now select the image and move it around as you like on the canvas...
(7) Go to the "Edit" menu and choose "Transform" then "Distort." You will see little boxes on the corners and on the sides. These are the areas you can click and move to manipulate the image. Just experiment with moving the image around until it looks the way you want. "Skew" and "Perspective" are also very useful for manipulation, so experiment with these features.
(8) If you want a drop shadow under the cover, double click the layer to get the pop-up menu called "Layer Style." Check the "Drop Shadow" box under the Blending Options on the left. To adjust the shadow (the default is not very good) click on "Drop Shadow" to the right of the checked box to reveal the Drop Shadow settings.
NOTE: If you have Keynote on the Mac, then you can ignore all this since the drop shadow settings within Keynote itself are wonderful — you can just add shadows later as you need them. (PPT has "shadows" too, but they are not good, natural-looking ones).
(9) When the cover looks the way you want it, then crop the canvas to cut out any extra area.
(10) Now choose "Save As" from the file menu. Save as a PNG file if you want the canvas area to be transparent. If you want the area around the cover to be white (because your slide background is white, for example) then save it as a JPEG. The advantage of using a PNG file is that you can place the cover into any kind of background and see only the book cover, not the canvas. If you choose to save it as a JPEG with a white (or any other color) canvas area, then the book cover will look good only over a white background where the canvas area appears to disappear. The advantage of JPEGs is that the file size will be smaller.
My explanation does not do justice to the procedure because it is actually very easy and fast – if it were time consuming or difficult I would not do it. And you can skip this entire process and insert the book without any manipulation, of course. In fact, if I am just showing a picture of the book cover, I do not change its shape at all. But if I have a quotation on the slide (and want to include a photo of the book) I can get a bit more space for the quote. Usually, the quote takes up two-thirds and the image one-third of the slide, more or less. This manipulation of the perspective of the book cover allows the cover to be a little larger while at the same time allowing more space for the quotation. All of this must be done without creating a feeling of crowding or noise, however, in the slide.