imageloadfont() loads a
user-defined bitmap font and returns an identifier for the
font (that is always greater than 5, so it will not conflict
with the built-in fonts).
The font file format is currently binary and
architecture dependent. This means you should generate the
font files on the same type of CPU as the machine you are
running PHP on.
表格 1. Font file format
See also imagefontwidth() and
imagefontheight().