Cannot delete a photo from icloud

While looking at my appleTV I noticed a photo that I want removed. I cannot see or delete that one photo on my iphone or ipad and when logging directly into icloud I do not see photos at all. I read some postings saying that if the sync was from a PC then I must delete it from the PC but the PC crashed. I think that there should be a way to login to the web interface for icloud and delete/edit/add photos directly.

How do I delete a photo on icloud?

How do I delete all photos from icloud?