Here's a great The Atlantic piece on sorting the photographic wheat from the chaff during Sandy.
"The fakes come in three varieties: 1) Real photos that were taken long ago, but that pranksters reintroduce as images of Sandy, 2) Photoshopped images that are straight up fake, and 3) The combination of the first two: old, Photoshopped pictures being trotted out again."The Guardian too have a blog going on collating these digital frauds and a few tips on how not to perpetuate rumour.
There are a few ways to spot modified or reused digital images. Geotags and EXIF data are of course a decent way of spotting the obvious fakes, but you can also use Google Advanced Image Search and TinEye to scour the web for previous incarnations of the latest 'exclusive' Sandy picture of a shark swimming through Brooklyn.
I had a great session with the BBC's UGC hub on this earlier this month. They're the real experts and their verification hub employs over 20 people, 24 hours a day to check photos and try and establish providence in storms of digital fakery.
Update: Plenty more fish in the sea, sharks in the suburbs etc...