Default cleanup edits supported container records. JPEG scan data, PNG IDAT data and WebP image chunks are retained rather than decoded and recompressed. File size can shrink even though the compressed image data stays unchanged.
Three different comparisons
A file hash will normally change when metadata changes. That alone does not mean picture quality changed. Conversely, an image that looks similar does not prove its compressed picture data was preserved. Separate three questions: did the file bytes change, did the encoded image payload change, and does the rendered image still look correct? A useful test report names the comparison it actually performed.
Why display information matters
Some information outside the main image payload affects interpretation or presentation. Color profiles and orientation are important examples. Transparency, animation, and format-specific structural data also need deliberate handling. PNG and WebP specifications distinguish different chunk roles; removing everything except a guessed picture block is not a safe general policy. A metadata-only operation still needs output validation.
A practical verification workflow
Work on an image you own or may modify and preserve the original. Choose a tool that documents its exact format and removal scope. After exporting, inspect the intended metadata fields, check the file opens without errors, and compare dimensions, orientation, color, transparency, and animation where relevant. A developer claiming unchanged payload should additionally compare the relevant encoded image data before and after, using representative fixtures for each supported format.
Do not confuse export with preservation
Drawing an image into a browser canvas and exporting it creates a new encoding path; it is not evidence that the original payload was retained. A lossless output format also does not establish that all source characteristics were preserved along the way. If a tool cannot demonstrate a narrower claim, use wording such as “metadata cleanup” rather than promising unchanged quality or identical pixels.
Can a cleaned file have a different size?
Yes. Removing metadata changes file structure and may reduce size; the amount is not a reliable quality test.
Does “lossless” mean all metadata is gone?
No. Payload preservation and removal coverage are separate claims that require separate checks.
