Market-data company IDC said recently that while it expected a potential recession to curb U.S. ad spending across all media by as much as 7 percent in 2008, quarterly online ad growth would still increase by around 15-20 percent in 2008.

"What happens is that the current economic crisis puts pressure on advertisers to save money and find more effective marketing channels," the report quoted Karsten Weide, programme director, Digital Marketplace and New Media at IDC, as saying.

"Effectively, the crisis accelerates the shift of advertising budgets from traditional media into new media."

IDC also forecast that U.S. Internet advertising spending will more than double in five years.

Martin Sorrell, the CEO of WPP, the world’s 2nd-largest ad firm, will moderate the "Cannes Debate" seminar where Microsoft, Yahoo and Google officials will discuss how the online world changes the way the ad industry operates.

Other Cannes high-profile attendees such as Publicis Chairman Maurice Levy, Havas Chairman Vincent Bollore, or media mogul Rupert Murdoch, are also likely to ponder the implications of Web pioneer Yahoo letting rival Google sell search ads on its site and of the failed talks between Yahoo and Microsoft.

The festival runs from June 15 to 21.

(Editing by Sue Thomas)