peace@peace:~/gsoc/online/loolwsd$ make
make  all-recursive
make[1]: Entering directory `/home/peace/gsoc/online/loolwsd'
Making all in test
make[2]: Entering directory `/home/peace/gsoc/online/loolwsd/test'
make[2]: Nothing to be done for `all'.
make[2]: Leaving directory `/home/peace/gsoc/online/loolwsd/test'
make[2]: Entering directory `/home/peace/gsoc/online/loolwsd'
  CXXLD    loolbroker
Util.o: In function `Util::encodeSubBufferToPNG(unsigned char*, int, int, int, int, int, int, std::vector<char, std::allocator<char> >&, LibreOfficeKitTileMode)':
/home/peace/gsoc/online/loolwsd/Util.cpp:254: undefined reference to `png_set_longjmp_fn'
collect2: error: ld returned 1 exit status
make[2]: *** [loolbroker] Error 1
make[2]: Leaving directory `/home/peace/gsoc/online/loolwsd'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/peace/gsoc/online/loolwsd'
make: *** [all] Error 2