PrivateMark does two things, on-device, no servers, no accounts. 1) Trace any leak. Before you share a photo, PDF, Word or PowerPoint, it weaves in an invisible, per-recipient watermark. If a copy leaks, feed it back and it names whose copy it was. 2) Hidden Photo. Send a picture everyone sees as an innocent cover; your trusted contact opens it in PrivateMark to reveal the real photo, sealed with AES-256.