When you scan deeply cracked photos there is a slight curve to them which creates a shadow/dark area near the crack

to fix this problem you might want to try this
1)take a white piece of paper the size of your scanner bed not glossy paper
and it must fit entire scanner bed

2)fasten photo to the center of the paper,then scan at whatever settings you
personally use

3) now turn the paper with the photo still attached 180 degrees and scan again DO NOT CHANGE ANY OF THE SETTING

4)bring both photos into photoshop turn the one thats upside down 180 degrees and layer them over one another DO NOT DRAG AND DROP to layer
because they will not line up,instead SELECT then EDIT/COPY EDIT/PASTE

5)adjust layers to taste

hope this is helpful Zganie

Thanks, Zganie! Very useful tip!

Oh, why you make so much trouble for your self?
Leave your glues and fasteners it is much easier.
Just change layer mode to DIFERENCE, then you will always line up.