As the built-in phone app doesn't support full screen caller images, you can relay on some third-party dialer apps. The one I prefer is called Eyecon. The app shows an ad on the after call screen occationally which is non intrusive. The best part is, this app will automatically download the contact image from Facebook. For eg. If your friends number is added to his FB account and the same number is saved in your phone, the app will automatically download it and save to your contacts. Also you can manually download the contact images directly from FB. This is just a suggestion, you can use any dialer app which support full screen caller id.
I forgot to mention, Eyecon won't work in some gulf countries as it is blocked. If you use a VPN it will work and you can verify your telephone number. Once verified, it doesn't need Internet connection to work and you can continue using it even without Internet.
