The Preview application has a Markup toolbar, which allows drawing over the top of an image. I was thinking about the possibility of using this feature to draw opaque shapes to redact sensitive portions of an image. My specific case is hiding names from a PNG screenshot.
This is on a version of macOS prior to Big Sur, so the "Redact Selection" option is not available in the app.
My intuition is that, as a raster-graphics image format, the resulting PNG wouldn't contain the redacted text even as non-visible image data. This differs from something like a PDF, where the data is still present in a layer behind the redaction, and therefore recoverable by examining the file data.
Can Preview be used in this manner to irrevocably remove sensitive information from a PNG image?