Scanner is a device to digitize printed material into computer-readable form. Digitizing data allows quick building of searchable databases, data mining or easy and fast research. Scanning books allows to quickly search, recall and share information, especially if someone has many, many books on the shelf. Many companies try to show book digitizing as theft - it isn't. I have books which were published in 100 or 500 copies. Ask any publisher for such book you e.g. lost in flood and you'll see how worth are all licenses to them.
But digitizing books takes time. Imagine you have 300-page book, which you scan with flatbed scanner, 60 seconds per sheet (2 pages, scanning, turning page, positioning, pressing button). 150 minutes if you're really quick and have no breaks or distractions. But usually scanners aren't so fast. Before e-book markets, e-book making was an important part of computer Scene. Polish groups (e.g. SCAN_DAL or UUK) used home scanners to transform books into high-quality OCRed ebooks, literally remaking the book, like typesetters and metrampagers did before printing. In early 2000s it took them even few weeks to "rip" a book completely.
In this text I present a quick-and-dirty version of a DIY book scanner based on a different principle. This scanner uses 2 cameras to take photos of 2 pages of a book simultaneously. It takes about 3-4 seconds if cameras need to focus. Next, platten is lifted, page turned, platten goes down (3 seconds), which takes ca. 7 seconds per 2 pages. In result, 17-18 minutes per 300-page book. If you have good cameras with constant focus, you can minimize picture taking time. If you get used to operation and "feel" the device, you can turn the page under 2 seconds. Camera-based scanners are very fast.
This documentation is based on ASCII file and contains ASCII drawings. The file has been made in my trusted HP 200LX palmtop after building parts of a scanner - it was not a plan, it was a log. There was no plan at all except "build something usable". Later, photos of a ready device have been taken to complete description and everything is now ported to HTML.
I don't know much how to make things of wood, I have only basic tools (except screw cutter, this is the most complicated tool) and I usually don't use calliper as much as I want. Everything except cameras comes from recycling or disassembly of old parts (mostly furniture). But it is still possible to make operable scanner with such resources.

 _________________________
|      |       v||v       |
|      |       v||v       |
|      | ===   v||v       |
|      |X======v||v     X |
|      | ===   v||v       |
|      |       v||v       |
|______|_______v||v_______|  <--Still part
     Moving part

In both photos there is sliding mechanism, camera column and unfinished crank mechanism. It is needed to use rod which doesn't deform on its sides when squeezed in its width. It is not needed to cover the "slipstick" from the top, as it slides smoothly and doesn't go upwards (in fact I had to stick a few layers of tape below to make it go a bit upwards to correspond with right side stator part).

First, find the largest nut with hole corresponding to screw on the rod. If you see it from its front, it looks like (hole omitted):

  _.....
 / \    |<-- a - nut's height
 \_/.... 

  ||
  |||_  <--A hinge, the angle of its opening is different than in this picture
  || \\
  ||  \\/ <-Bolt for camera
I=||===\\
  ||         I===== - Screw to precisely set angle.

The base is a small wooden block, about 5x20cm, the hinge is fastened to its shorter side. In the end of this block a hole for camera bolt is drilled and camera bolt is screwed. A rubber washer (like in a water tap valve) is applied to secure the camera and mount it in proper rotation.
The other arm of hinge is mounted with at least two bolts to holes in column. To make it movable don't use screws, but nuts and bolts.
It is important to maintain the proper horizontal angle of the board not to tilt the camera.
To properly tune the camera, mount it and watch is the bottom of its picture parallel to the spacing between plates.
After proper setting of camera, it's needed to drill additional hole for a big and long screw ("I=====" in the picture) - it will be used to keep the angle of camera and eventually correct it.

One arm seen in front. Dots are edge of the arm in far. Comb in the bottom.
Step 2 2: Cutting "V" in the "Comb":

_____  ____
_____\/____

   _______
  |   |   |
  |   |   |
 ||   |   ||
 ||   |   ||
 ||===|===||

To fix the glass to bar, use the following "sandwich"

======
|DDDDDDD <-A wooden strip (e.g. from floor panel)
|XXX     <-Window foam pad
|ZZZZZZZZZZZZZZZZ <-GLASS SHEET
|XXX     <-Window foam pad
======

======
|DDDDD <- A wooden block protected with insulation tape
|DDDDD 
|ZZZZZZZZZZZZZZZZ <-GLASS SHEET
|XXX     <-Window foam pad
======

The platten should be squeezed to keep 90-degree angle using wide cable ties. In the angle sharp glass edge can easily cut the ties, so use piece of aluminium (e.g. from cans) to protect it.
To these large ties, fix the U-shaped metal bar to easily lift the platten to turn pages.

View from front:

  _____________ <--Cable tie goes around
 \\          //
  \\        //
  O----------O  <--U-shaped handle kept with cable tie
    \\    // 
     \\  //
      \\//   
       \/ <--Cable tie goes tot he edge of glass, protect it!

Remember to glue foam pads on stator, the way that they won't collide with a book. They prevent platten glass from scratching.

  Pipe
---   ---
| |   | |
|_|   | |
 _____| | <-Hole for cable
|       |
|       |

From top:
 _____
|  :  | <- Hole for cable (unseen, drilled in wood)
|  O  | <-Pipe nest
|_____|

3 wall surface switches are used. 2 are single, they turn light bulbs on and off, one is double. It turns on the power supply for cameras and a socket for computer.

Power supply unit consists of few parts. Transformer (TRAFO) gives 7-8V at 1,5-2A. It is rectified in Gretz bridge (G) and smoothed with electorlytic capacitor (>1000uF per camera). This voltage is linearily regulated using LM317 tunable regulator to the voltage required by cameras. There are two regulators for two cameras (useful if there are 2 different ones).

It is VERY important to connect grounding wire to sockets. Switching power supply units don't like sockets without earthing.

In many cases it is needed to add a small fan to cool linear regulators, in my unit it's running from linearily-regulrate 5V supplied from transformer. It's a small-power 12V fan, under 5V it runs quietly but efficiently.

Remember, the power disspiated by the linear regulator is ca.: P = (Uin-Uout)*I Where: Uin - input voltage, Uout - output voltage, I - current drawn.

1. Get wires which connect Return key from your keyboard. It requires to dismount keyboard and use e.g. small socket for it. In my small PoS keyboard there was a space for small Jack socket. And it is needed to figure out which pins of IC are shorted when Return is pressed. "Shorted" means even 130 Ohms between them, because foil has its resistance. For protecting chip ports, if you have measured some significant resistance, add some to your connector.

2. Use PCB from old keyboard, connect proper wires and connect this keyboard as second one (two USB or one USB and one PS/2 keyboards may be used the same time).
The button is mounted in a small piece of plastic to platten's handle. Wires are going along platten's edges to its back. Presing button links proper keys and it results in pressing Return. For solution 2 it looks like:

Button      Connectr ____PCB
 \--------------<>--|____|------------[PS2-USB converter]---USB in computer.

Thanks to connector, we can remove platten for cleaning.
I've used second solution first (see photo 2 on the right), then switched to first solution as more elegant and less demanding from PC.

In general, scripts for losslessly rotating 10MPix JPEG files (not to be confused with EXIF rotating which is changing few bytes in JPEG contrary to matrix transpositions and lossless recompression) are very slow on 64MB of RAM. Linux is a system with memory management different than Windows, DOS or some older Unix systems. If there is a memory unused, Linux will use it to speed things up, storing frequently accessed data in special buffers. If some program wants to use more memory, buffers are just freed - memory is used, but system runs slowly. So if you add more memory, you'll in most cases just get faster system. 10MPix photo requires 30-40MB of memory to be processed, if it's processed optimal way, and in Open Source tools it may not be. When 64MB of RAM are installed, most of it (ca. 50MB) is used by system services (Display, console, network) and processing program, so not much is left for photo. Buffers, in such situation, do not exist. That's why the system must use disk-based space (swap) which is much slower. Generally prefer >=128MB computers, because 64MB is really slow.

To operate scanner, special scripts are needed. I've made Bash scripts to use both in general-purpose machine or in specialized embedded PC configured for scanning only.
Here you can download shell scripts in two variations:
1. "On-demand" - an universal script for taking photos, acquiring images and separate script for joining from two cameras. It can be used in higher resource systems used not only for scanning.
2. "Environment" - is a complete environment written in Bash and Dialog to take photos, acquire, join and send to USB drive or FTP server. This software can be used in embedded systems.

Start with bootstrap.sh. It will check for Dialog presence, make Buffer directory in Your home folder and start operation greeting with WELCOME.MSG contents. Then it will display menu, as shown in the picture.