Why do some items like JFIF and pHYs stay in the file after I clean the photo?

Three states in the list

After you press 'Remove metadata', the tool re-scans the output file and shows every item from the original with one of three marks: 'Removed' for what went, 'Stays' for what the tool deliberately keeps, and 'Remains' for an item that should have gone and is still there. You should never see the third; if you do, the tool tells you not to rely on the file. This post is about the second.

What stays in a JPEG, and why

• The JFIF header: it holds the format version and the pixel density, such as 72 × 72 dpi. Some programs need it to know how to read the file, and nothing in it is about you.
• The Adobe color transform marker (APP14): it tells the decoder how to turn the channels into colors. Removing it can make some images decode with completely wrong colors.
• The ICC color profile, if you chose to keep it, which is the default.

What stays in PNG and WebP

• pHYs: the suggested print resolution, such as dots per inch. Technical information for printers that reveals nothing about you.
• iCCP, gAMA, cHRM, sRGB and cICP: chunks that describe color, always kept in PNG because they define how the image looks.
• The VP8X flags in WebP: they describe what the file contains, such as transparency or animation, and the tool updates them after removal so the file stays valid.
• ANIM animation data in animated WebP, and any chunk the tool does not know. Removing an unknown chunk could break the image, so it is left in place and listed by name and size.

Reading the list with confidence

1. Open the photo in the Image metadata inspector and remover tool. Before removal each item is marked 'Will be removed' or 'Stays', so you know in advance what will happen.
2. Press 'Remove metadata' and go to the 'After removal' list.
3. Check that everything carrying information about you, such as EXIF, GPS, XMP and text fields, is now marked removed.
4. Review what is left: if it is all of the kinds listed above, the file is clean of personal data.

The 'nothing to remove' message

Sometimes you open an image and find only JFIF, or just pHYs and sRGB, and the tool says the file has nothing it can remove and the items shown are needed to display the image. That is good news: the photo was clean already, and there is no need to download a new copy.