的 png_info 结构从删除 png.h 1.5.0，现在你应该使用这个指针与 png_get _ * 和 png_set _ * 功能。

The png_info struct was removed from the png.h in 1.5.0 and now you should use this pointer with the png_get_* and png_set_* functions.

如的libpng手动：

的png_info结构被设计成提供有关的信息
  PNG文件。有一段时间，png_info领​​域的用意是
  直接访问给用户。然而，这往往会导致
  使用动态加载的库问题的应用程序，并作为
  结果为png_info一组接口函数（该png_get _ *（）
  和png_set _ *（）函数）的开发，并直接进入
  png_info领​​域是德precated ..

The png_info structure is designed to provide information about the PNG file. At one time, the fields of png_info were intended to be directly accessible to the user. However, this tended to cause problems with applications using dynamically loaded libraries, and as a result a set of interface functions for png_info (the png_get_*() and png_set_*() functions) was developed, and direct access to the png_info fields was deprecated..

例如：

png_uint_32 height;
height = png_get_image_height( png_ptr,  info_ptr);