What are the critical and ancillary chunks in a PNG file, and which ones can I safely modify to hide data without breaking the image?

PNG files are composed of data chunks. Critical chunks like IHDR, IDAT, and IEND are essential for rendering the image; altering them usually breaks the file. Ancillary chunks (e.g., tEXt, zTXt, gAMA) are optional and can be deleted or modified without affecting image display. For example, the `tEXt` chunk (textual data) allows embedding arbitrary text, making it a perfect place to hide secret payloads. This technique is covered alongside LSB Steganography in PNG Files for more covert approaches.