STRPTR name = GetImageFormat(APTR handle);
HWEXT_IMAGE_FORMAT
extension bit has been set. See Extension plugins for details.
If that is the case, this function must return a null-terminated string
containing the name of the format of the image file handle passed in handle. The
string returned by this function can be retrieved from Hollywood scripts by querying
the #ATTRFORMAT attribute on image-based objects like #BRUSH or #BGPIC. The string
you return must be valid until FreeImage() is called on the image handle
passed to this function.