1. Jailbreak iPhone 3GS (PwnageTool) or 3G (using redsn0w0.9.5b5-5).
2. Install OpenSSH via Cydia.
3. Connect your iPhone with your Computer and SSH into it.
Install either CyberDuck for Mac or WinSCP for Windows.
Get your iPhones IP address from Settings > WiFi > Name of your network provider.
Here are the login details to SSH into your iPhone.
For CyberDuck:
Server: IP address of your iPad/iPhone.
Protocol: SFTP
Username: root
Password: alpine
For WinSCP
Hostname: iPad IP address
Protocol: SCP
Username & Password: Same as for Cyberduck.
After you SSH into your device, be sure to change the password from the default alpine using the passwd command.
4. Next copy the plist file from your device to your Computer as follows:
iPhone 3G: /System/Library/CoreServices/SpringBoard.app/N82AP.plist
iPhone 3GS: /System/Library/CoreServices/SpringBoard.app/N88AP.plist
5. In the Capabilities section of this property list file, add a key named hdr-image-capture with a boolean value of true.
6. Save the file and copy this modified property list back to your device via SSH replacing the older version.
7. Restart Springboard or reboot your device, and you should now see the HDR setting in your iPhone camera app.