There are several ways you can use of to remove those pictures from your phone. After connecting your phone to your computer, open up "iTunes" go to the photo tab and uncheck the box for Syncing them into the phone, once that's done, sync iTunes to your phone. The second way to get it done is to remove it manually from the phone, but since it seems like the pictures was synced to your phone from iTunes, you will not be able to remove it manually from the phone, so only iTunes is your choice here, unless you jailbreak, then you can use other software to remove those pictures from your phone.