With this image Descartes is trying to show how everyone's view of things can look like a different object or logo. For example from someone else's perspective they might see a company logo, the top of a filled tub of popcorn, or just a cloud. This image is related to irrefutable truths because no matter what everyone will always see a different object, though most might say its a cloud, others might say it looks like something else, so there will always be a doubt over what the image actually is due to perspectives. This relates to existentialism because of how each human will see a different object in this image or any other image. 
Perspectives 

• cloud
• soundcloud logo
• Popcorn
• other company logo's