First, you'll need a jailbroken iOS 4.1 for the next steps. I know, the Jailbreak for 4.1 is not out there yet. So, stay tuned.
B.If you have an iPhone 3G, grab the file located at /System/Library/CoreServices/SpringBoard.app/N82AP.plist
C.If you have an iPhone 3GS, grab the file located at /System/Library/CoreServices/SpringBoard.app/N88AP.plist
D.Add a key named “hdr-image-capture” with a boolean value of “true” to the “capabilities” section of this property list
E.Save it, and use SSH to replace the copy on the device with your modified version
F.Restart SpringBoard, or just reboot your device. You should now have access to the HDR setting in the camera application.