I use Photoshop for my image manipulation. I am no scanning or Photoshop expert but here are some guidelines that seem to work for me.
- Always align item squarely on the scanner. This means that the scan won't have to be rotated later, and thus lose some quality. Ensure item and scanner bed are very clean.For photos, wipe clean with a clean, dry, soft cloth. Don't be tempted to breathe on them as this does bad things to photos.
- Get item as flat as possible on the scanner bed; a heavy book helps, but make sure it is only one colour so that it does not show through the item being scanned.
- Scan with 300 dpi. (note: dpi is not significant for the web; it is the total number of pixels. dpi is only important for printing).
- Save it uncompressed in a lossless format (e.g. tif) on your computer.
- Save a second file of the scan as a .jpg file with moderate compression. The balance is between retaining a high quality of scan and a moderate file size; in Photoshop something like "8" seems to work well usually, and gives a file size of around 300K.
- There is one scanner setting that I somethimes find useful. It is called descreen on my scanner. Magazine pictures are made up of a screen of dots, and often these cause problems when scanning at the same sort of resolution as the dots. Selecting the descreen option on your printer can OFTEN (not always) help to give a better image. It does this internally in the scanner, by kind of blurring surrounding dots together. This gives a better picture but is now slightly blurry. This can still be okay, but often I find that I need to double the dpi to be used for scanning when descreening is used. I then use Photoshop to bring the scan back to half the dpi again. This sharpens up the scan. Photoshop can even be used to sharpen the image further if necessary.