GIMP (the GNU Image Manipulation Program) is a great product. It provides many advanced image editing options and is available on both the Linux and Windows platforms. Of course, it is FREE. One capability that is noticed to be missing from its sizable suite of tools is a “deskew” function. As the name suggests, a deskew function straightens up a somewhat crooked picture. This is often needed to straighten up a scanned image that did not pass through the scanner in a perfectly straight manner. After quite a lot of searching on the web, I found that there is a plugin (an add-on) that provides this function for GIMP. For the typical user, getting ones hands on the deskew plugin is not as easy nor is installing it intuitive, so I will provide links to both the Linux and Windows versions of the deskew plugin and instructions how to install each.
First download the plugin for your OS:
To install in the plugin into GIMP for Windows, unzip the plugin from the file you downloaded and place the deskew.exe file in the c:\program files\gimp\lib\2.0\lib\plug-ins\ folder.
To install the pluging into GIMP for Linux, simply place the pluging you downloaded, the deskew file, into the /usr/lib/gimp/2.0/plug-ins/ folder.
Now, either open GIMP or close and restart the program if you already had it open. You will now find a new entry in the Filters menu called Misc. The plugin is selected via the menu path Filters>Misc>Deskew.
NOTE: I did not write the GIMP deskew plugin, and thus cannot provide any support for it. I just want to make it easily available to other GIMP users since it took me some time to find both versions.