We shouldn't judge early about this.but seems to require Windows XP Service Pack 2 (SP2)
The input is an extension like ".bmp".it doesn't tell me what to do with that information either.
The outputs are in this case PERCEIVED_TYPE_IMAGE, perceived flag = 22 (not quite sure about this one) and "image".
So it seems the function is useful to get the perceived type from an extension.
Based on this information you could select the "image" key mentioned in the first post of this thread in read the necessary information to open the file successfully.