Not what one would call a leisurely boat ride . . .

According to Snopes.com this photograph is genuine and was taken from a September 2005 Africa Geographic article titled "Shark Detectives," about researchers studying Great White sharks off the coast of South Africa. As the article described the circumstances under which this picture was snapped:
Sitting in a 3.8-metre sea kayak and watching a four-metre great white approach you is a fairly tense experience. Although we had extensively tested the sharks' reactions to an empty kayak and had observed no signs of aggression, this gave us little comfort as we eyed a great white heading straight for us, albeit slowly. Just a metre or so from the craft it veered off, circled and slowly approached from behind. It did this several times, occasionally lifting its head out of the water to get a better look. Then it lost interest, and as it continued on its way we were able to follow a short distance behind. Once we'd come to terms with having nothing between ourselves and a four-metre shark except a thin layer of plastic, our kayak made an ideal research platform for observing great white behaviour in shallow water. Its advantages are twofold: it is inconspicuous and appears not to cause the sharks to alter their behaviour for long, and it allows us to watch them in a natural situation, as it is not necessary to attract them to us with food. (http://snopes.com/photos/animals/sharkkayak.asp)