As we can see there's still shadows left on the scan.
Step 1 --> Click with your mouse on the 'Marquee tool.'
Step 2 --> Select with the marquee tool the shadow area.
Step 3 --> Go to Layer --> New Adjustment Layer --> Levels. Step 4 --> Play a little with your numbers and hit on ctrl, + to zoom in at at least 50%.
These are the numbers I use.
As you can see, I leveled it too much. *oops*
Don't worry, I've done this on purpose. *laugh*
Step 5 --> Click on the "Eraser Tool'.
On your screen you should see a toolbar for brushes.
Step 6 --> Click on the arrow like the below given example.
Step 7 --> Change the diameter of your brush to 70px.
Step 8 --> Change the opacity of the brush in 40%.
Step 9 --> Go with your mouse to the pattern below on the scan. Step 10 --> Click on your mouse, hold it like that and start to erase parts of the level-layer. Like this.
Step 11 --> Let go of your mouse at 'end'. Step 12 --> Repeat this one more time.
Step 13 --> Set the diameter of your brush this time to 20px.
Step 14 --> Scroll up a little like this example.
If you start to erase it just like we did earlier, you get to see this.
Therefore I don't end it at the end of the scan but more like this.
Step 15 --> When you're done set the opacity this time to 10%.
Step 16 --> Now erase the last part of the scan. This should be your end results.
Step 17 --> Go to Layer --> Flatten Image.
Step 18 --> Set the opacity of your brush back to 100%.
Step 19 --> Make sure your background color is white.
Step 20 --> Zoom in your scan at 100% and erase the dust at the white background.
Step 21 --> Scroll all the way up. As we can see there's still some dust left.
Step 22 --> Click with your mouse on the Polygonal Lasso tool.
Step 23 --> Select with the polygonal lasso tool the dust area.
Step 24 --> Go to Layer --> New Adjustment Layer --> Levels. Step 25 --> Play a little with the numbers for the input levels. These are the numbers I use.
And the dust is gone.
Step 26 --> Select your eraser brush and take a look at the whole scan. If you find any dust, please remove it.
Once you're done, this is how your scan should look like.