Sometimes I need to process scanned images or photographed book covers, where I usually only have the resulting image (JPG/PNG) but not the original (to recreate a clean variant myself). Pages/covers are not always correctly aligned, which is the hardest task of post-processing for me currently: it's a complicated job in Gimp using the "perspective tool", as I've found no alternative to that yet.
Seeing scanning apps on Android, it should be pretty easy to adjust/align such a scanned page:
As the screenshots show, you basically tap the 4 corners of the paper (or rather adjust the "grid" to match them), tap the check-mark in the toolbar (at the bottom), and have the page adjusted.
What's possible on some smartphone with Android shouldn't be too hard to accomplish on a more powerful desktop machine. Nevertheless, either my Google-Fu isn't good enough or there doesn't seem to be a corresponding application.
Summing up my requirements:
- must run on Linux (Java applications acceptable, Gimp-addons welcome)
- must be free (as in "free beer" – open-source would be an added plus)
- easy to install (not too many dependencies)
- easy to work with (basically, as easy as it is in mentioned Android apps)
- can be stand-alone or an addon for Gimp