Photos/Videos imported from computer using iTunes or other software are stored in Photo Library. Either iCareFone or iPhone/iPad can only delete photos stored in Camera Roll.
If you cannot delete photos with iCareFone, please try the following methods:
If you have synced photos with iTunes before, please try to turn off Sync Photos option in iTunes first. Simply connect your device with iTunes, and click on the device icon, then select Photos > uncheck Sync Photos option.
Hope this guide helps. If above operations cannot solve this issue, please try to reconnect the device and try again.