I have installed Whatsapp through Bluestacks on my laptop. I have also installed Dropbox for both Bluestacks and laptop separately.
Please open Dropbox on Bluestacks, log in with the same username and password you use to log in on the PC and manually upload the pictures. You can find Whatsapp pictures in the Gallery folder titled as Whatsapp.
For iPhone, use AppToCloud: https://itunes.apple.com/app/id993386131.
This app was made to allow users to copy multiple image and video files from WhatsApp (and others) to Dropbox, Google Drive or OneDrive for iPhone, iPad e iPod.