HandL - Label data for machine learning with ease
digiKam - Professional Photo Management with the Power of Open Source
Fused - Create stunning double-exposed photographs in seconds
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
VSCO Cam - VSCO Cam is an iPhone, iPod Touch, & Android camera app w/ elegant, minimal processing options.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.