What Are PNG Chunks?
A PNG file is made up of a signature and a sequence of "chunks" - each chunk is a named block of data with a 4-character type code. Critical chunks like IHDR (image header) and IDAT (pixel data) are required for the image to display. All other chunks are optional and carry supplemental information.
Software like Photoshop, Lightroom, iOS and Android add metadata chunks - tEXt, iTXt, eXIf - alongside the pixel data. These chunks are invisible to the viewer but can expose camera model, GPS location, author name, creation date, and editing software to anyone who inspects the file.