ACDSee - ACDSee is an image viewer that uses very little system resources, and it has a small, sleek size that won't take up much space on your system.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
digiKam - Professional Photo Management with the Power of Open Source
Photos on macOS - Photos keeps your images organized and accessible. Rediscover favorite shots with Memories. Access them on your devices with iCloud Photos.
Flickr - image and video hosting website
Fileloupe - Media Browser - Fileloupe is a lightweight, incredibly high performance media browser for macOS. You can quickly browse photos, watch videos, read PDFs and preview documents all within the same window. It's like the Finder's Quick Look window, only better.