pngcrush caught libpng error

While reading /***/***.png pngcrush caught libpng error:

   Not a PNG file..

Could not find file: /***.app/***.png

Command /Applications/Xcode.app/Contents/Developer/usr/bin/copypng emitted errors but did not return a nonzero exit code to indicate failure

该文件不是真正的png文件，多是个jpg文件，实际的文件头信息是不同的，形成不能识别。