Smarty plugin / modifier

Hi all.

In my templates, i use a lot of <img src="pixel.gif" height="1" wifth="1">
......
How can i make modifier / plugin for this ... like :
{p} .... ordinary pixel.gif wiht widtht=1 and height=1 -- default values
{p:10:5} .... pixel.gif with width=10 and height=5

... sorry if this isnt maillist for plugins/...

Greetz.