Opt-out signals sit at several levels: robots directives, headers, per-file metadata and registry-based mechanisms. Coverage is inconsistent and enforcement is mostly reputational rather than technical.
For a studio the relevant question is usually the client’s, not the crawler’s. Some clients want their campaign imagery excluded from training corpora, and the honest answer is that you can express the preference reliably and cannot guarantee it is respected.
Say that plainly in the brief. Promising an enforceable opt-out is a claim about other people’s behaviour that nobody in this supply chain can actually make.
Can you stop your imagery being used to train models?
You can express the preference through the available signals. You cannot guarantee it is honoured, and any supplier promising otherwise is making a claim about third parties they cannot control.
Should opt-out be in the brief?
If the client cares about it, yes, along with an honest statement of what is enforceable and what is a request.