IN A MOVE THAT POTENTIALLY cuts down on click fraud, Google today is expected to announce that it will now allow advertisers who participate in AdSense to purchase inventory on a cost-per-thousand impression basis, rather than cost-per-click. The search giant also will announce today that AdSense advertisers may now purchase ad space on the sites of specific publishers, and also serve image ads through AdSense. The upgrades, currently offered in beta to a select set of Google advertisers, will be rolled out to all Google advertisers within the next few weeks, a Google spokesman said. Advertisers will be able to select specific Web sites on which to place their ads, and then set a cost-per-thousand impression bid, as opposed to paying on a cost-per-click basis. Google already calculates likely cost-per-thousand impression prices by looking at cost-per-click and click-through rates.