In the U.S., a model release is generally about using a person’s identifiable name or likeness, especially for publicity/appropriation concerns. If the subject is truly not identifiable in the final image, that usually weakens or removes the need for a release based on likeness alone.

That said, this is not a blanket guarantee. Other privacy-related claims can still matter depending on the content and context. For example, even if a person is not recognizable, an image could still raise issues if it reveals private facts or is otherwise intrusive.

Separately, you generally own the copyright to photos you create unless an agreement says otherwise, so copyright and model-release issues are different questions.

For portfolio display, exhibition, or selling prints, the key issue is whether the person is actually identifiable and whether the image creates any other privacy problem. If they later change their mind, that does not automatically give them the right to block use of a non-identifiable image, but specific facts and local law can change the outcome.

Because this is a legal question and can vary by jurisdiction and by the image content, consult a qualified attorney if the use is important or commercially sensitive.