optipng

TLDR

Compress a PNG with default settings

$ optipng [path/to/file.png]

Compress a PNG with the best compression

$ optipng -o[7] [path/to/file.png]

Compress a PNG with the fastest compression

$ optipng -o[0] [path/to/file.png]

Compress a PNG and add interlacing

$ optipng -i [1] [path/to/file.png]

Compress a PNG and preserve all metadata (including file timestamps)

$ optipng -preserve [path/to/file.png]

Compress a PNG and remove all metadata

$ optipng -strip all [path/to/file.png]