digiKam - Professional Photo Management with the Power of Open Source
Screenshotlayer - Screenshotlayer is a lighweight REST API built to deliver PNG, JPEG & GIF website screenshots at unparalleled speeds.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
LICEcap - A straightforward, high performance application that enables users to capture a portion of the desktop and save it to . GIF or . LCF, LICEcap is available for download as a GPL free software.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
ShareX - ShareX is a free and open source program that lets you capture or record any area of your screen...