In May of 2004, Google launched image ads on their content network, where advertisers could ad image ads in their normal adgroups and they had the "possibility" of showing up in the content network ads.

Today, Google announced that they will expand this feature by allowing advertisers to setup site targeted campaigns that will display image ads on a cost per impression (CPM) basis instead of their standard cost per click. For the first time advertisers will be allowed to specify which sites their ads will appear on. Additionally, Google announced they will start allowing animated images, which had been restricted in the past.

Full details are not yet available, as the service hasn't officially launched. It doesn't appear that Google will be opening this selective targeting option up to their standard PPC content targeted ads.

This move could open up more opportunities for content publishers to earn more money through the Google Adsense.

Google's content network has been affected heavily with click-fraud, causing many advertisers to turn off content networking.

Impression Fraud, where unscrupulous publishers need only generate web traffic to their site, might be even harder for Google's system to police since they won't receive the data typically sent with a click. My guess is that this fear was the main driver of the decision to offer site targeting for these ads. For this reason, I would caution advertisers wanted to run CPM ads to only select high-profile sites that you are familiar with.