- don't try to build when jpeg support is not available

examples/nnquant.c

@@ -23,6 +23,7 @@ void save_png(gdImagePtr im, const char *filename)
 
 int main()
 {
+#ifdef HAVE_JPEG
  	gdImagePtr im, im2;
 	FILE *fp;
 	char path[2048];
@@ -56,5 +57,9 @@ int main()
 	save_png(im, "a_jquant_dither.png");
 
 	gdImageDestroy(im);
+#else
+	printf("JPEG support is required for this example. Please recompile GD with JPEG or change this example to use another format as input.");
+	return 1;
+#endif
 	return 0;
 }