Command line image manipulation

Dear Experts,

Is it possible via command line to rotate an image automatically so it is perfectly straight?  For example, lets say I scan in a document and the scan is slightly at an angle because the document was not inserted into the scanner properly.  I know you can rotate the image using something like this:

convert -rotate 90 input.jpg output.jpg

But is it possible to automatically detect how much it needs to be rotated by to straighten it up?

Thanks
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narmi2Asked:
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narmi2Connect With a Mentor Author Commented:
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Kruger_monkeyCommented:
There is a way to have it rotate if the size meets criteria x.

See here.

http://www.imagemagick.org/script/command-line-options.php?ImageMagick=hjg5196r7dlcfpti6df137psp5#rotate
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narmi2Author Commented:
I can't figure out from that link how the program can automatically detect how much to rotate the scanned document to straighten it up.
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Kruger_monkeyCommented:
I'm not sure how automatic it is based on your needs but the section that may be of use is the following.

as it says if you add -rotate -"90>" it will rotate and image if the width is more than the height. It's only automatic based on the criteria of either width less than height (>) or if width is less than height.

-rotate degrees{<}{>}
Apply Paeth image rotation (using shear operations) to the image.  

Use > to rotate the image only if its width exceeds the height. < rotates the image only if its width is less than the height. For example, if you specify -rotate "-90>" and the image size is 480x640, the image is not rotated. However, if the image is 640x480, it is rotated by -90 degrees. If you use > or <, enclose it in quotation marks to prevent it from being misinterpreted as a file redirection.

Empty triangles in the corners, left over from rotating the image, are filled with the background color.

See also the -distort operator and specifically the 'ScaleRotateTranslate' distort method.
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narmi2Author Commented:
Here is an example scan image I want to straighten up

http://www.jonbenetindexguide.com/10131999-HunterGJ-Announcement-Pg2.gif

As you can see, this is slightly tilted.  Can the above commands straighten this up without me telling it how much to straighten it up by?
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