You absolutely don't care about some of those details in the background. The pictures will never be seen except on a computer monitor Other Comments 1. There is no advantage in scanning color photographs at a resolution higher than the optical resolution. If the original photograph is faded, set the black and white points to the white side of the range, if possible. The rules here apply to scanning photographs for archival purposes.
Different rules apply to web pages or desktop publishing.
To overcome the pixel straddling effect. I put this one first because it is not well understood and is also the most important. Let's imagine that you have a picture whose resolution you are sure of. For example there is a picket fence far off in the background. If you just match that resolution when you scan and the scanner dot sensors happen to each exactly straddle a fence picket and the empty space between pickets, you get a total blur.