Some of the images in the "photography" gallery are actually scans. When digital cameras were still new (2 megapixels...) scanning was the method to digitise image at highest quality. And today scanning is probably still producing the least noisy images. When i can scan it - i will.
Scanners have a few narrow depth of field, as if you were photographing with a macro lens.
Here are a few tips i found useful and discovered over time:
1.) Scanning Dirty Things
When scanning dirty materials, protect your glass with a thin transparent foil, i use those that are used for overhead porjectors (although this gives a slight morire). The foil also allows me to scan fluids. To fix the fluid in one place i fill it into an empty looroll that is placed on the foil. If you want a high Depth Of Field you fill in more, i want only sharp bubbles fill in little... very dependent on your materials
2.) Scanning Flowers
A favourite scanning subject. But to get the best results let it hang head over. If you put the flower head down on the scanner, the leafs would bend very unnatural. Therefore i set up a system that allows me to hang the flower above the scanner, so that it BARELY touched the glass. By moving the rope i can precisely ajdust the distance between scanner and object AND the object will not move at all.
3.) Multi Pass Scanning
You can somtimes achieve interesting effects if you scan the same object with different setting (dont change/move the motif!!!) and then layer these together in your image editing software. This is a bit like rendering the same object with different materials and then combining in PS. Quite Experimental but worth a try.
Try to optimize your image inside your scanning software as far as possible so that further manipulation in your image-software is kept to a minimun, because every change via Levels/Curves will redcue you image's quality.
[EDIT 2010]: These days modern camera have also come to include this method. They call it bracketing or HDR (high dynamic range), taking several photos of the same motif with different exposures. Try manual HDR with your scanner!