% brew install pngcrush % pngcrush -n -v hoge.png | pngcrush 1.7.60 | Copyright (C) 1998-2002, 2006-2013 Glenn Randers-Pehrson | Portions copyright (C) 2005 Greg Roelofs | This is a free, open-source program. Permission is irrevocably | granted to everyone to use this version of pngcrush without | payment of any fee. | Executable name is pngcrush | It was built with libpng version 1.5.16, and is | running with libpng version 1.5.16 - May 23, 2013 | Copyright (C) 1998-2004, 2006-2013 Glenn Randers-Pehrson, | Copyright (C) 1996, 1997 Andreas Dilger, | Copyright (C) 1995, Guy Eric Schalnat, Group 42 Inc., | and zlib version 1.2.8, Copyright (C) 1995 (or later), | Jean-loup Gailly and Mark Adler. | It was compiled with gcc version 4.2.1 Compatible Apple LLVM 4.2 (clang-425.0.28). Opening file hoge.png for length measurement Allocating read structure Allocating read_info, end_info structures While measuring IDATs in hoge.png pngcrush caught libpng error: Not a PNG file..