Images are a problem because they interfere with copy.  

Ever hear the phrase, "a picture is worth a 1,000 words"?  It comes from the Chinese proverb,  "A picture's meaning can express ten thousand words,"  which means that both words and pictures can be worth 10,000 of the other.   Take for instance, the opening line to a joke, "A man walks into a bar."  Those words evoke images even though the bar is not actually described.  Is it a biker bar?  Is there a bartender?  What does the man look like?  Are there people in the bar?    

The problem is not with pictures or words, but in how the two are typically mixed in advertising. 

University of Wales researchers reported in 2005 that each of us experiences around 3,500 advertisements a day, or about one every 15 seconds, including ads on billboards, television, in store, radio, magazines, and direct mail.  The research also showed, however, that under 1% of these advertisements can be recalled without prompting the next day. 

That same year, a report from University College London decribed finding that once the brain has started to focus on a communication (an ad, a letter, a radio commercial), there is a decrease in the person's ability to focus on another communication for a short period afterwards. 

Taken together, the research suggests that any ad has to grab attention, but the message must be so clear and easy to comprend that the recipient can actually focus on your message—and therefore block out the next ad attempting to steal away your receipient's attention.

Some advertisers have set their holy grail as the being the really attention-grabbing image.  Yet the scantily-clad model probably becomes the focus and the advertiser's name and product offer become the competing message that the mind can't quite focus on just yet.

Therefore, the whole traditional approach of advertising (grab attention, then sell the product) really doesn't work unless the "grab attention" and the "sell the product" are very well intergrated.  Avoid the flash, particularly the attention-grabbing image, keep everything simple, and let your medium be the message.   Are you selling personal services such as banking? Send a personal letter, not a fancy brochure.

Start the brain off with a picture and the words become a distraction.  Start the brain getting interested in text first, then use your pictures to support your copy.