Glitching PNGs

PNG, the classiest just-works web image format, offers unique opportunities for glitch art—all flowing from the fine details of its specification.
PNG is a very simple format compared to JPEG or other new image formats. The filter algorithms are like toys, and its compression method is the same as oldschool Zip compression. However, this simple image format shows a surprisingly wide range of glitch variations. We would perhaps only need one example to explain a JPEG glitch, but we need many different types of samples in order to explain what a PNG glitch is.
PNG was developed as an alternative format of GIF. However, when it comes to glitching, GIF is a format that is too poor to be compared with PNG. PNG has prepared surprisingly rich results that have been concealed by the checksum barrier for a long time.
Mandatory: