From the article on Crazy Egg:
“It is easy to see why this is becoming a regular practice among websites, it gives your site a very sexy look.
A good looking website is one of the first aspects of your site that your visitor responds to, both consciously and subconsciously. The background image, when used appropriately, is an easy way to give your site a sleek look without compromising major real estate.
A well-known conversion killer is stock photography, and the mega image trend requires companies to invest in quality, original photography. With a renewed focus on how photography impacts conversions, the mega image trend has eliminated one of the long-time conversion faux pas.”
It is sometimes easy to look for the cheap way out. And with all the free imagery out there, it is simple to find free and very cheap images.
But if they do not work for your website and actually drive people away, their value becomes contradictory – and they become a liability. One you chose.