An image scanner can make great pictures of circuit boards. Not only are the pictures clear, they are very high resolution and have nearly perfect scaling. Perfect scaling means that you can actual make measurements from the image. Try that with a digital camera!
I picked up the pictured Artec scanner for about $20 some time ago. It is close to useless and takes the worse scans I have seen. But even so, it can be used to make usable PCB images.
This image shows the bottom side of the graphics LCD I am giving away (details in this post). You can clearly read the IC part numbers and some of the other part values. The image shows a bare PCB.
If you grab the high res version (just click on picture) you can see more detail. The parts of the LCD PCB which were not against the glass do not look so good. Trust me this is due to the way this specific scanner works. If you have a good scanner the image will stay in good focus for about ¼ to ½ inch. With normal scanners the image is in focus for a good distance but detail is lost as things are further from the glass.
To make these scans all you have to do is place the PCB on the glass. You should put the cover down on the scanner to block outside light. You could also turn the lights out in the room. Some scanners do not work well without a background. To get really good scans you may need to block the light that could enter around the sides of the cover. It is also very important to keep the PCB level with respect to the glass.
To make measurements from the scans, you need to figure out what the pixels are per inch or what ever units you want to use. I like to use mils and this scanner at 300dpi has about 2.4 pixels per mil. You can find the scale by measuring a known distance on the PCB. The selection tool in most programs will tell you the pixel length of the selection box. You maybe able to set the resolution in your program so you can read your selection sizes directly.