Best web app no doubt. But I just noticed an issue with the latest version. If you use any file manager (file manager, filebox, etc.) you're unable to open pictures through the file manager. After I unistalled the app I was able to open the picture. It's very reproducible as I have repeated the bug multiple times.
This might explain why i can't open received image on Wazapp/open image using Filebox...i'll give this a shot. EDIT : Yes, I confirmed that Opera is giving this problem