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I believe users get too much information from the image ad and don't feel the need to click to read more.
From a publisher POV, I don't like them -- as an advertiser they are probably good for low cost branding, (e.g. - design an ad that gets your brand name, site name or product info out -- if nobody clicks them, you don't pay).
If you want to generate clicks, user "leader" type messages, e.g.-
Want to know more about _______ ?
What our competitors don't want you to know...