Deskew is a command line tool which can detect skewed text in scanned text documents, and output a straightened version.
The program can import and export BMP, JPG, PNG, GIF, TGA, PSD, TIF and a few other file types, depending on platform.
The command line interface means Deskew is more awkward to use than we'd like, but don't be put off entirely- it's still probably easier than you'd expect.
The download includes sample images, for instance, and a RunTests.bat batch file which processes them. Run this, check the results, then open RunTests to see how it works.
The sample commands can be as simple as this.
deskew -t a -a 5 -o TestOut/Outa1.tif ../TestImages/1.tif
The -t sets a threshold value, which is set to "automatic" here so doesn't require any knowledge. The -a value sets a maximal skew to consider of 5 degrees, which again can probably be left, and the other arguments provide output and input file names.
Brief details on these and other commands are available in a Readme.txt.
Deskew did an excellent job of straightening our test scanned pages. You might need to spend a while setting up scripts or batch files to run it properly, but if that's not a problem we'd say it's worth the effort.