I am constantly revising these instructions, based on my own experience, and on the images people send me. Here is the latest version (subject to future revisions).
Do NOT use the scanner's own cover when scanning knives or other 3D objects.
Instead use a large piece of paper, to cover the knife and the *entire* glass.
Usually white paper works best. Or light gray. Or sometimes tan.
DO NOT EVER use colored papers, or textured materials. Same rule applies to photography, unless you are a professional advertising photographer and know how to light the background separately.
Also try varying the angle of the knife lying on the glass, since the light of the scanner is directional. Make sure shadows do not fall on important details, such as markings.
If you are ambitious, raise the paper above the knife and glass on a frame, to darken the background and put it out of focus. Downside: requires much more dust spotting of each scan.
Scan at monitor resolution, either 96 or 100 dpi, NOT HIGHER (unless the scan is for magazine publication -- then follow their specs). 96 dpi is the maximum that any monitor can display; some older scanner offer 100 dpi, but newer ones offer 96 dpi. Use it!
Unsharp masking ON (usually a checkbox). This improves figure/ground separation.
Descreening ON (usually a menu item). This minimizes 'jaggies.'
Scan full knives at 100% size or larger. For very large knives, make multiple overlapping scans WITHOUT rotating the knife.
Always crop out empty background in the pre-scan, before the final scan.
Scan TIGHTLY CROPPED closeups of details such as markings at 300% size or larger, big enough to read easily.
Save each scan to disk in its original format (my Epson scanner makes .TIF files).
If posting pictures to a website, or sending them by email, DO NOT USE .TIF or other raw files.
Convert them to compressed JPG format, using any image editing program.
I use ThumbsPlus, free download from www.cerious.com
These programs let you do color and contrast corrections, dust spotting, and other fixes. They even let you add captions and labels to the photos, and create composite images.
When saving JPG files, you will be offered compression options.
Choose 2:2 subsampling and 75% quality. These are the maximum settings that a monitor can display. Any higher setting wastes bandwidth. Any lower and you'll start seeing 'tile' artifacts.
Use the corrected and CROPPED JPG files for websites and email.
* * * * *
A digital camera can work, too, if you use it correctly:
For knife photos:
1. plain smooth light gray background.
2. diffuse light -- cloudy daylight or a white ceiling. Do not use on-camera flash.
3. use a tripod or other solid camera support.
4. use low resolution, suitable for monitor, not print
5. Do NOT use "electronic zoom." It only makes the pixels larger, not the image.
6. CROP OUT empty background!
As with scans, convert image files to .JPG format, 75% quality, 2:2 subsampling.