WARNING ======= Libpng 1.5 erroneously uses /MD when building debug DLL versions of libpng. It should use /MDd - you can change this under properties\C/C++\Code Generation\Runtime Library if you need to use the debug runtime for debug builds. This will be changed in libpng 1.6 but is currently retained for compatibility with older libpng 1.5 releases. The runtime library settings for each build are as follows: Release Debug DLL /MD /MD Library /MT /MTd The Visual Studio 2010 defaults for a Win32 DLL or Static Library project are as follows: Release Debug DLL /MD /MDd Static Library /MD /MDd Notice that by default static library builds use the DLL runtime, not the static library runtime.