The KDE way
There are many image-processing applications that integrate specifically into the KDE Plasma desktop environment and are worth mentioning. The KIPI-Plugins is a modular system that powers different KDE-related applications, such as the Gwenview image viewer and Digikam, and enables the impressive list of destinations where you can upload your photos. The Dolphin file manager can be extended using extra services that reside at http://kde-look.org. Go to Configure Dolphin > Services to upload new stuff right from within Dolphin,eg KDE Services is a Swiss Army knife-style tool, and it includes a graphics converter and resize/rotate tool that work in Dolphin’s right-click menu.
There’s a great standalone application called Converseen that has a rich set of converting and resizing options for images. Converseen is based on Magick++ libraries and supports more than 100 image formats. It’s a perfect tool for bulk actions with advanced features. Photo retouching is rarely done in KDE-centric applications, but you can happily do it in Krita. Even though Krita is focused on digital art, there are both Clone Brush and Healing Brush engines in brush settings, which enable you to remove objects and fix undesired effects. Go to Filter > Adjust and select the proper tool for fixing colour levels, hue, colour balance and other things that potentially can improve your photos. The Filter menu has many more options, not as many as there are in the Gimp, but still enough for highquality photo retouching.