When you scan stuff that is white like paper etc just slip in a piece of coloured card behind it. Make sure it covers the whole scanner bed. I use a red cardboard file folder i had floating around. I find red a better choice than black because then when I clean up the scan I dont accidently select back shadowed areas in the folds of the paper

You should be scanning at 300ppi too

- Scanning at 300ppi will give you 1:1 image (eg a 5x4 photo will still be a 5x4 photo. If its something small scan at 600ppi to get a 1: 2 result (eg a 5x4 photo will become a 10 x 8 photo)
HTH