Flickr - image and video hosting website
CThruView Transparent Image Viewer - CThruView is a free transparent image viewer that allows mouse clicks to go through the image.
Imgur - Imgur is a free and simple image hosting service with image editing feature. Signup is optional.
LayerX - An intuitive app to display transparent images on screen.
PhotoPrism.app - PhotoPrism® is an AI-Powered Photos App for the Decentralized Web. It makes use of the latest technologies to tag and find pictures automatically without getting in your way. You can run it at home, on a private server, or in the cloud.
Osiva - Osiva" is an acronym that stands for "Overly Simple Image Viewing