preg_replace an image

[LMimo]

I want to output a random number (1 to 40) and to output an image associated with the number.

I have sorted the first part with...

<![CDATA[$this->post['message'] = preg_replace('/\[picturenumber\]/i',mt_rand(1,40),$this->post['message']);]]>

But, I am unsure of how to use preg_replace to also add the associated image. Any ideas?

Thankyou

[Analogpoint]

If your images are names 1.gif, 2.gif etc:

$img = '<img src="path/to/images/'.mt_rand(1, 40).'.gif" alt="" />';
$this->post['message'] = str_ireplace('[picturenumber]', $img, $this->post['message']);