Image manipulation in GNU/Linux has always been associated with The Gimp. However, most users will find Gimp vastly oversized for their needs. Fotoxx is a neat, simple and yet very advanced photo manipulation software that is definitely worth installing and playing with.
Ubuntu's repositories carry a rather old version of Fotoxx. So, I strongly advise you download the latest version of fotoxx from Kornelix.com. The latest one available, 15.05, has a much improved interface and is more stable.
I won't get into the detail about installing a package; however, Ubuntu users should be OK with just double-clicking on the .deb file.
When you first start up Fotoxx, it will ask you to locate the folder with your images. Fotoxx will then create a searchable index of them, very much like most of other image processing programs.
Using the program: photo manipulation
I am the least artistic person, and was able to create several funny images starting from a photo of my wife.
Manipulating an image is really fun -- especially when the victim is your own unsuspecting wife. The effects are really, really simple to use and understand. Plus, they always offer a live, real-time preview of what they will show.
Undo/redo has a slightly unconventional pattern: left mouse click will undo, and right mouse click will redo.
In general, the user guide is really well written and comprehensive. You can get to it by pressing F1. I recommend you read it if you want to discover how to use these rather advanced, and yet simple, effects! There is a one-page document, also reachable from Help > Quick Start, that has a quick summary of how to use Fotoxx.
Reading the first few pages of the user guide is not optional!
I don't like using bold fonts in articles. However, this is so important, it cannot be underestimated. The software's author is very clear about this: it takes a little while to get used to it, and it diverges (slightly) from what you normally see from programs. However, this is not necessarily a bad thing -- it's just something you need to keep in mind.
Using the program: gallery
Fotoxx can be used as a gallery manager. It also comes with a World Map. I have to be honest: the use of these functionalities is beyond the scope of this review. However, you are certainly most welcome to play with them.
The editing abilities of Fotoxx are enough to make it a must if you want to be able to edit your photos and have professional-like results in no time.
Here is a list of capabilities, taken straight from Fotoxx's guide itself:
Thumbnail browser / navigator with variable size thumbnails and list view.
Camera RAW file conversion with retention of 16 bits per color.
Internal processing in 24 bits per color (float), image file output in 8 or 16 bits.
A comprehensive set of image edit, retouch and repair functions: brightness, color, contrast, tone mapping, trim, resize, rotate, de-noise, paint, clone, red eyes, write text, warp, HDR, panorama, art effects ...
Select image areas or objects, edit separately from background, copy and paste.
Rapid visual feedback using the full image or selected zoom-in area.
Metadata editing and reporting (tags, dates, captions, geotags, ratings ... )
Batch tools for file renaming, resizing, converting, adding and revising metadata.
Search images using any metadata, directory / file names or substrings.
Geotag mapping and reporting by location or by clicking on a geographic map.
Create albums (collections or "views") with images from various directories.
Montage: arrange images and text in an arbitrary (huge) layout.
Slide show with various animated transitions, image zoom-in.
Comprehensive user guide and help popups.
Update since publishing the article: I've been communicating with Fotoxx's author as well as Richard Miler, a Fotoxx user; I was asked honest feedback on how to address some of the issues I raised in the original article; well, I did -- I spent a good couple of hours working out all of the usability issues I could find, and sent it to Fotoxx's author. My email followed a lengthy discussion with him. My work was appreciated: Fotoxx's author has addressed all of the issues I raised (!) which did, no doubt, take a lot more than a couple of hours to fix!. The changes are in the July 2015 release of Fotoxx. After 20 years of free software, I had never experienced such prompt action stemming from my comments. Thanks! End of update