This is the first time I've put images next to the edges of the pages in my books. I understand that that the printer may cut 1/16 inch off the pages, so that's why I let the images slightly overlap the edges. Is a bleed necessary?
Not only you need bleed, but you need to consider if you need to shift the image a bit away from the borders depending on the binding method you are using.
Saddle stitching binding allows the book to lay flat when it is open. The content that is close to the inside edge of the book will be visible. This method of binding is usually expensive.
Perfect binding books are glued at the spine so, when it is open, the middle of the book buckles. How much it buckles depends on how many pages it has. A portion of the content that is close to the spine will be hidden or difficult to see. This method of binding is usually cheaper than saddle stitching.
Take this into account when setting up an image that will cross over the inside edge of the book. If it is a saddle stitched book then just make sure that the image is trimmed at the same spot in the facing pages and provide extra bleed beyond this spot.
This will not work for perfect bound books, as you can see in the image below. The curved area in the inside edges will give the illusion that the image is distorted.
If your book is perfect bound, then you have two options:
- Method A: Shift both images so, after they are trimmed and bound, they give the illusion of a continuous image. How much the images need to be shifted depends on how many pages your book will have and where the image falls in the page count. Ask the printer for their opinion. This is a very tricky and risky method.
- Method B: Move the image so the focal point is not in the middle of the book and the distortion is not so noticeable. Even if the image is missing a chunk, the reader will not notice it.
The purpose of bleed is to mitigate imprecision. The printer "may cut 1/16 inch off the pages" means that the printer will not guarantee that their cutter will be accurate within 1/16 plus or minus (a 1/8 inch range).
So the question for you is not about cutting too much off, but whether you will be happy with a sliver of white paper showing when they don't trim enough. If you don't want to see white paper, then a bleed is required.