Image Links vs. Text Links
http://www.uie.com/brainsparks/2006/01/16/image-links-vs-text-links/

Spool, Jared M.
User Interface Engineering
2006

Abstract:

Years back, we compared successful clickstreams (clickstreams that resulted in users accomplishing their goals, as observed in tons of usability tests) with unsuccessful clickstreams (clickstreams where users abandoned their goals before completing), looking for any clues that would help us predict behaviors in one that we didn’t see in the other. One factor we looked for was whether the clickstreams contained image links versus text links — does one type of link show up more often in successful clickstreams than the other. Our finding was when users clicked in image links they were just as likely to succeed or fail as when the clicked on text links. There was no statistically-meaningful difference.