TL;DR
macOS doesn’t offer native per-image password locks in Preview, but you can secure pictures using built-in tools without third-party apps. Two practical approaches are creating an encrypted DMG in Disk Utility or converting the image to a password-protected PDF via Preview.
What happened
The article outlines two no-extra-software methods to protect sensitive images on macOS. The first uses Disk Utility to create an encrypted virtual disk (a DMG) from a folder containing your images: Finder > Applications > Disk Utility > File > New Image > Image from Folder. When making the DMG you can pick its name, destination, encryption level (up to AES-256) and image format; choosing Read/Write lets you add or remove files later. The main tradeoff is having to mount and unmount the disk each time. The second, faster method leverages Preview: open the image in Preview, choose File > Export as PDF, then click More Details > Permissions and enable “Require Password To Open Document” and set a password (an owner password is also requested). This produces an encrypted PDF (Preview uses AES-128), after which the original unprotected file can be deleted and the trash emptied.
Why it matters
- Screenshots and saved images can expose banking, tax or other sensitive details if left unprotected on a Mac.
- Both Disk Utility and Preview let users add encryption without installing third-party software.
- AES-256 (available for DMGs) offers a higher key size than the AES-128 used for PDF encryption in Preview.
- The Preview method is faster for single images, while a DMG is more convenient for managing multiple files over time.
Key facts
- Preview does not provide file-level password protection for image files directly.
- Disk Utility can create an encrypted DMG from a folder via File > New Image > Image from Folder.
- When creating a DMG you can select encryption up to AES-256 and choose formats like Read/Write or Compressed.
- Read/Write DMGs allow adding or removing files later; Compressed images are read-only by default.
- Converting an image to a PDF in Preview and enabling Permissions lets you require a password to open the document.
- Preview’s password-protected PDFs use AES-128 encryption.
- Creating an encrypted PDF requires entering a password and an owner password even if not sharing the file.
- After producing the encrypted file, the original unprotected image should be deleted and the trash emptied.
What to watch next
- Threat actors are increasingly adopting AI techniques to scan files regardless of filenames — consider encrypting sensitive images rather than relying on obscure names (mentioned in the source).
- Mounting and unmounting an encrypted DMG each time you need files may be inconvenient for frequent access.
- Differences in encryption strength (AES-128 for Preview PDFs vs AES-256 for DMGs) may influence which method you choose depending on sensitivity.
Quick glossary
- Disk Utility: A macOS app for managing disks and disk images, including creating encrypted DMG files.
- DMG: A macOS disk image file format that can be encrypted and mounted as a virtual disk.
- Preview: macOS’s built-in app for viewing images and PDFs; it can export images as PDFs and add PDF permissions.
- AES-128 / AES-256: Advanced Encryption Standard with 128- or 256-bit key sizes; larger keys increase the number of possible combinations.
Reader FAQ
Can I password-protect an image file directly in Preview?
No. Preview does not lock image files directly; you can export the image as a PDF and then apply a password.
Do I need third-party software to encrypt images on a Mac?
No. The source describes two built-in options: Disk Utility for encrypted DMGs and Preview for passworded PDFs.
Which encryption strength is used for each method?
Disk Utility DMGs can be created with up to AES-256; password-protected PDFs created via Preview use AES-128.
Is it necessary to enter an owner password when making a protected PDF in Preview?
Yes. The export screen requests an owner password even if you do not plan to share the file, per the source.
iOS 26 has three new iPhone features I’ve been really loving Ryan Christoffel Dec 29 2025 MAC PRIVACY SECURITY BITE Security Bite: How to quickly password protect image files on…
Sources
- Security Bite: How to quickly password protect image files on Mac
- Password Protect Files on a Mac: 4 Quick and Easy Ways
- How to Password Protect Folders and Individual Files on Mac
- Password-protect a Pages document on Mac
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