Eric Raymond documents two already-existing functions (bmp, png).

gvanrossum · gvanrossum · commit dfba2fbfd0ea · 1998-07-17T19:01:29.000Z
diff --git a/Doc/lib/libimghdr.tex b/Doc/lib/libimghdr.tex
@@ -28,6 +28,8 @@ \section{Standard Module \module{imghdr}}
   \lineii{'rast'}{Sun Raster Files}
   \lineii{'xbm'}{X Bitmap Files}
   \lineii{'jpeg'}{JPEG data in JIFF format}
+  \lineii{'bmp'}{BMP files}
+  \lineii{'png'}{Portable Network Graphics}
 \end{tableii}
 
 You can extend the list of file types \module{imghdr} can recognize by
