anchor.diff:      "ZINC=${zlib}/include"
       "ZLIB=${zlib}/lib"
     ];
  +
  +  passthru = {
  +    srcVerification = fetchurl rec {
  +      inherit (src)
  +        outputHash
  +        outputHashAlgo
  +        urls;
  +      failEarly = true;
  +      pgpsigUrls = map (n: "${n}.asc") src.urls;
  +      pgpKeyFingerprint = "8048 643B A2C8 40F4 F92A  195F F549 84BF A16C 640F";
  +    };
  +  };
   
     meta = with stdenv.lib; {
       description = "Portable Network Graphics (PNG) optimizing utility";
  
positive.code: }:
  
  stdenv.mkDerivation rec {
    name = "pngcrush-1.8.4";
  
    src = fetchurl {
      url = "mirror://sourceforge/pmt/${name}-nolib.tar.xz";
      sha256 = "4ef6d790677cf57f622db693337d841b60d62c044e8681299245c298bd56161a";
    };
  
    buildInputs = [
  
negative.code:     zlib
    ];
  
    postPatch = /* Fix hardcoded install prefix */ ''
      sed -i Makefile \
        -e "s,/usr,$out,"
    '';
  