I use an HP 6200C flatbed scanner, and I am running Windows ME on my computer. For quick and dirty scans, I use the Windows scanning wizard, which has the following interface:
The scanning program will try to guess the type of picture, and as far as I can tell uses default brightness and contrast levels, although you can alter them in the advanced properties box above. Note that you can set the scan resolution in the properties (which while this shows 150 dpi, I would actually scan at 300 dpi for this photo). Note also that HP makes their own scanning drivers, but I'm not using them currently because they keep threatening to destroy my USB ports when I try to install them (not particularly WinME friendly, I guess). Using the advanced dialog box above, I would set the brightness (too much pure white? turn it down) and contrast (not enough levels between the darkest shade in the image and the lightest? turn it up). Usually between adjusting the controls, you can get a reasonable scan, but it involves a lot of guesswork.
Below is the scan taken with the scanner set at the default values (my original scan):
Note that the light areas are washed out, and the black clothing is closer to a mid gray. Take a close look at both faces - there is evidence of posterization (i.e. like a poster, what would normally be a smooth gradient of tones is represented by a series of large changes of tones - such as the pure white cheek highlights suddenly transitioning to the very dark grey cheek shadows. For another example of posterization, see here.). This cannot be completely blamed on the scanner and software, part is due to the original photo being scanned.
On the next page, I'll show you a couple of ways of dealing with this photo.