I don't think you'd be able to take down a website with this strategy. The OPs site never went down, it just cost him a lot of money. Even pretty small webserve

I don't think you'd be able to take down a website with this strategy. The OPs site never went down, it just cost him a lot of money. Even pretty small webservers should be able to serve up static image files pretty easily. But you could do a denial of service by making the service too expensive and all of your work would be hidden behind the anonymity of the google bot.