Exported from a design tool for a public blog post. This is an illustration — no real file, name or location is used.
Before — what you would be sending
diagram-final.pngPNG
Authora.whitfield
TitleQ3 margin model — CONFIDENTIAL
SoftwareFigma export 2026.7
Last modified 14 Aug 2026
After cleaning
diagram-final-clean.pngPNG
Authorremoved
Titleremoved
Softwareremoved
Colour profile and transparency preserved. Only descriptive text is dropped.
PNG stores metadata as chunks
A PNG is a sequence of labelled chunks. Some are essential to displaying the image. Others hold free text: an author, a description, a comment, the software that saved it, sometimes a full EXIF block copied in from a camera.
What is kept
Only the chunks that affect how the image renders: the header, palette, transparency, colour profile, gamma and the image data itself, plus animation chunks for APNG files. Everything else is dropped.
A common source of surprises
Diagram and design tools often write the project name, the file path or the licensed user into a text chunk on export. Screenshots edited in a desktop app pick up the same thing. It never appears anywhere in the picture, so it is never noticed.
In practice
The chunk structure, briefly
A PNG is a signature followed by a sequence of chunks. Each chunk states its length, a four-letter type, its data and a checksum. Chunks whose type begins with a capital letter are critical to displaying the image; lowercase means ancillary. Text and timestamp chunks are all ancillary, which means a decoder that skips them still renders the image perfectly. Cleaning a PNG is therefore a matter of copying the critical chunks and the rendering-relevant ancillary ones, and dropping the rest.
Where design tools leave their mark
Export a PNG from a design or diagram tool and it will often write the document name, the artboard name, the tool version and sometimes the licensed user into a text chunk. None of it appears in the image. Diagram exports are a frequent source of internal project names reaching public blog posts, because nobody thinks of a PNG as a document with properties.
What must be kept
Not every ancillary chunk is safe to drop. Gamma, chromaticity, sRGB and embedded colour profile chunks all affect how colours are rendered, and removing them can visibly shift the image. Transparency and animation chunks are essential to APNG files. A cleaner that drops everything ancillary produces a file that looks wrong, which is why the list of what to keep matters as much as the list of what to remove.
Common questions
Do PNG files have EXIF data?
They can. The format has a dedicated chunk for it, and some tools copy EXIF across when converting from JPEG.
Will stripping chunks change how the PNG looks?
No. Colour and rendering chunks are preserved. Only descriptive text and timestamps are removed.