For those not familiar with PhotoQt, this is a fast, Lightbox-style Qt5 image viewer which uses GraphicsMagick under the hood (so it supports over 80 file types).

Besides its image viewing capabilities, PhotoQt can be used for some basic image manipulation (flip, rotate, zoom) and file management (rename, delete, move, copy).

gThumb is an image organizer/viewer that can export images to PicasaWeb, Facebook, Flickr or Photobucket, comes with some basic image editing features such as cropping, resizing, rotation, image enhancing, has video support, supports WebP images, can import images from digital camera and many other cool features.

gThumb 3.3.2 in Ubuntu 14.04 (under GNOME Shell)

Ubuntu 14.04 had gThumb 3.3.1 in its official repositories at some point but because starting with version 3.3.0, the application uses header bars (also known as client side decorations) and they don't work properly under Unity, gThumb was downgraded to version 3.2.7. And that's ok for Unity but how about Ubuntu GNOME and Linux Mint 17 (with Cinnamon 2.2.x) users?

Well, to make it easier to install, I've uploaded the latest gThumb 3.3.2 in the WebUpd8 gThumb PPA for Ubuntu GNOME 14.04 and Linux Mint 17 with Cinnamon users.

The application has been updated recently, getting a window mode (previously it was full-screen only) along with other interesting changes. Also, the application now uses GraphicsMagick which means it supports 80+ file types.

Photo is an image viewer in which the image is displayed in full-screen with a configurable, semi-transparent overlay behind the photo if it doesn't cover the whole screen. 

The application also features image thumbnails on the bottom, which are set to autohide in the new version, but you can set them to always be visible from the settings. The menu is also hidden by default and to access it, you must point the mouse to the top right edge of the screen. 

Besides supporting most popular image formats like gif, jpeg, png, bmp, tiff, xpm and so on, Photo can also perform some basic image manipulation like rotating, flipping or zooming, display exif information and comes with a beautiful interface. When opening an image, you can quickly switch to another image in the same folder by using the thumbnails displayed at the bottom: