The haunting images displayed in a photo exhibit at San Francisco City Hall claim to document the devastating effects of more than three decades of oil extraction in Ecuador's Amazon rainforest... Humberto Piaguaje...blames [Chevron] for sickening his people and poisoning his homeland. He's one of 30,000 plaintiffs in a class-action lawsuit that alleges San Ramon-based Chevron Corp. failed to clean up billions of gallons of toxic waste dumped in pristine rainforest in Ecuador... Chevron, one of the world's largest oil companies, has denied human rights and environmental violations in the 180 countries where it operates, but allegations of abuse threaten its public image around the world... Investors don't appear to be worried... Fadel Gheit, a senior energy analyst at Oppenheimer & Co., believes the company will likely win both cases [the Ecuador case and a US case related to alleged complicity in human rights abuses in Nigeria], and if they are forced to compensate victims, the payments won't be big enough to affect the bottom line. "It's nothing but background noise," Gheit said. But critics say the company's troubles in Nigeria and Ecuador are part of a deeper problem. [also refers to Texaco (part of Chevron), PetroEcuador, Talisman, Unocal (part of Chevron)]