Undefined symbols for architecture x86_64:
  "_png_create_info_struct", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_create_read_struct", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_create_write_struct", referenced from:
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_destroy_read_struct", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_destroy_write_struct", referenced from:
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_get_IHDR", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_get_valid", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_init_io", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_read_end", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_read_image", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_read_info", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_read_update_info", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_set_IHDR", referenced from:
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_set_expand_gray_1_2_4_to_8", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_set_filler", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_set_gray_to_rgb", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_set_longjmp_fn", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_set_palette_to_rgb", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_set_sig_bytes", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_set_tRNS_to_alpha", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_sig_cmp", referenced from:
      cimg_library::CImg<unsigned char>::_load_png(__sFILE*, char const*, unsigned int*) in test-78d9b2.o
  "_png_write_end", referenced from:
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_write_image", referenced from:
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
  "_png_write_info", referenced from:
      cimg_library::CImg<unsigned char>::_save_png(__sFILE*, char const*, unsigned int) const in test-78d9b2.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)