I must say, if I turned around and saw this, I'd probably crap my pants.

No, it doesn't look like any prey they'd normally feed on. Now, body boarders, with their legs and feet hanging off, look an awful lot like a sea turtle, believe it or not. They get chomped on a couple times a year, seems like. Surfers too, to an extent. Never heard of a shark attacking a kayak.Would a shark naturally go after the kyak like that in the first place?
That picture is not photoshopped,it's been around for a while and it's real.
This past summer my buddy and I fished for small bluefin tuna off Georges Bank off the coast of Mass.There are always 50-100 boats out there trolling for tuna.On three occasions boats reported that large white sharks would come in and grab the whole tuna that was hooked.I personaly know one fisherman who runs an 18 foot center console. He had hooked a school size tuna (60-120) pounds and as the tuna starts circling under the boat a 20+ foot white shark raced in grabbed the tuna, shook a few times and cut the line right off! The radio chatter was reporting 2 whites in the area, a 16 footer and a 20+.(WE need a bigger boat)
The same day another boat released a tuna and a great white raced up and grabbed it. Same day another fisherman gaffing a small tuna got pulled overboard.He was ok and joked about it,until he found out later what was going on!
They normally don't bother the boats but on occasion they go after the hooked tuna which are giving off vibration and blood in the water.