Sorry for the stupid question.
I red the answer on the official website http://dlib.net/compile.html Don't know what is "add all the source files in the dlib/external folder into your project " . Can someone give a screenshot? If I just put paths of the four folders in "additional include directories", I will get link error.
A answer here may works in VS2013 how to load jpeg file using DLIB libarary?. In 2015 there is no library branch as shown in the screenshot.
DLIB_PNG_SUPPORT and DLIB_JPEG_SUPPORT have been defined .
I built the examples with default cmakelist, then ran the facedetectionex. It still didn't work when I input a jpeg image.