iPhone 4 Tips - Remove Photos Imported From PC

Last few days, I accidentally imported some unwanted photos from my dad's pc into my iPhone4. There's around 590 photos imported. The annoying thing is that those photos cannot be removed like any other photo taken using iPhone4 itself (I'm using iOS 4.2.1). However after some googling, I found a solution in a forum discussion.

Basically, what we need to do is just to re-sync our iPhone using iTune by choosing some settings as highlighted in image below:

After selecting the settings, go to File menu on the top left menu and choose "Sync ..." and that's it. The photos are being removed!

Just wonder why those photos cannot be removed the same way as the photos taken using iPhone itself. A little bit annoying and disappointed.