BASALT · JOURNAL
How to check a PDF for hidden images before sharing
A PDF page can contain image objects outside the visible crop, beneath another object, or clipped by a mask. Those objects may preserve a scan, signature, screenshot, or personal detail that is not apparent in normal viewing.
Inspect page composition
Review pages at high zoom and look for masks, clipping boundaries, optional content groups, and objects outside the media box. Compare the rendered page with the text and image objects when the document contains sensitive material. Cropping or covering an image is not the same as removing it.
Use a release-copy workflow
Remove unnecessary objects rather than relying on visual overlays. If you need a static record, export a clean copy and inspect the new page structure. Keep the original separately for records and preserve page dimensions needed by the recipient.
Verify with search and visual review
Search for redacted terms, inspect thumbnails, and zoom into every marked region. Check attachments, comments, OCR, and metadata. Reopen the result in a viewer that does not share state with the editor used to create it.
Frequently asked questions
Can hidden images be recovered from a cropped PDF?
Sometimes. If the underlying image object remains in the file, a different viewer or extraction tool may reveal it.
Is placing a white image over content secure?
No. It hides the appearance but may leave the original object underneath.
Do scanned pages have hidden layers?
They can have OCR, annotations, masks, or embedded originals in addition to the rendered scan.
Doing it in Basalt
Basalt helps remove hidden page content and verifies the exported PDF locally, so the release copy contains only the material you intend to share. Download Basalt.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.