Smoke or Cloud
This image illustrates the sometimes blurred boundary of smoke and clouds, where one can bleed almost seamlessly into the next when the cloud layers are low enough to allow for it. Can you tell where the fire smoke ends and the clouds begin? (Source)
Also from Webist Media: WebUrbanist, featuring abandoned places, brilliant buildings and world wonders and from Webist's founder see architecture, interiors and fantastic furniture at Dornob and find great gadgets, strange science and tech with a twist at Gajitz
.
