WARNING ======= Libpng 1.6 does not use the default run-time library when building static library builds of libpng; instead of the shared DLL runtime it uses a static runtime. If you need to change this make sure to change the setting on all the relevant projects: libpng zlib all the test programs The runtime library settings for each build are as follows: Release Debug DLL /MD /MDd Library /MT /MTd NOTICE that libpng 1.5 erroneously used /MD for Debug DLL builds; if you used the debug builds in your app and you changed your app to use /MD you will need to change it to /MDd for libpng 1.6. 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