Not being able to opt out, and changing the system wholesale overnight like this, is deeply unethical.
On the scale of things they could do that would make this better:
* Best case: opt-in only, compensate users whose photos they use.
* Present a choice to users when they sign up, default to opt-out.
* At least present a choice to existing users whether they want this or not, and allow them to continued access to the service either way.
* Notify users and only change the rights when any new photos uploaded, and keep existing photos under the old terms.
* Give existing users the opportunity to deactivate/delete their account if they don't agree, and a chance to download their photos. Or "freeze" existing accounts until they acknowledge the changes, rather than automatically assuming consent.
They seem to have picked the absolute worst option available to them, and it's troubling to say the least.