Someone came up after our presentation today and informed us about IMEID's - "International Mobile Equipment IDs". Apparently, regardless of the SIM card used, every cell phone has a unique identifier which the server can request of it at any time. Here's some more info:
This means that the strategy we had in mind for preserving anonymity (after all others seemed infeasible) of suggesting that users throw out their SIM cards after uploading incendiary data will not work. The users would have to throw out the whole phone, which might be economically infeasible.
So back to square one with anonymity. It may be necessary to rely on phone-based encryption, which definitely stands out in a crowd. Perhaps we can figure out some mechanism for using steganography to hide incriminating media in non-incriminating.