Your Choice of format...

Use this for GIF (recommended):

<A HREF="http://contiki.ld8.org/guide/"><IMG SRC="http://contiki.ld8.org/guide/images/CTKOK.gif" ALT="[CTK+] Optimized For Contiki" WIDTH="88" HEIGHT="31" BORDER="0"></A>

Use this for PNG:

<A HREF="http://contiki.ld8.org/guide/"><IMG SRC="http://contiki.ld8.org/guide/images/CTKOK.png" ALT="[CTK+] Optimized For Contiki" WIDTH="88" HEIGHT="31" BORDER="0"></A>