Here's a quick and easy photoshop tip for you that will save you an endless amount of headaches if you don't already know about it.
How to straighten out crooked scans.
Tired of meticulously aligning your page on the scanner only to have it look infuriatingly crooked when you scan it?!?
Fuggeddaboudit. Here's how to fix it easy in photoshop.
1. Under your eyedropper tool is a ruler tool. Select that.
2. Find a level line on your scan. In comics, this is usually a border edge.
3. Click on one end of the border and drag the cursor across the page. As you move the curser you should see a line forming behind it. Let go of it on the other end of the border that you want straightened out. This should lock the line in position along your crooked border.
4. Go to Image>Rotate Canvas>Arbitrary. A value and direction will already be decided based on your ruler line. Click OK.
TA DA! Your image is nice and straight! Crop it to the proper size and you're done. You can thank me later by buying me a beer.