Thanks for getting back to me. Some background: I'm one of the volunteers at Distributed Proofreaders (http://www.pgdp.net/c/default.php)
We take old books and convert them into e-books, plain-text, epub, mobi, html, etc. But we always start with images of the pages. I've deleted the one that was giving me trouble but this is the sort of image that causes a lot of grief.
Nope, not allowed to add an image either! Here's the PhotoBucket link: http://smg.photobucket.com/user/Mebyon/media/Ebooks/015_before.jpg.html?sort=4&o=13
That's a bit exaggerated but you can see what I'd like to do; return the page to a rectangular form by dragging top left and right corners out. It's not so very important for the OCR as Abbyy FineReader would cope quite well with that text but illustrations need 'squaring up' all the time.
Paint.net looks like a perfect solution for us, (well, at least us who use Windows), as we're all doing this work for nothing and paying for PhotoPaint or PaintShop isn't really called for!
I just hope that there's a plugin for the sort of distortion repair that I'm looking for.
Thanks for your time.
Chris