bbcode replacement with image in posts

[tassoman]

Hi all,
I'm trying to replace a fixed bbcode with a random image, but i get instead a bbcode for that image. I would to display html of the <img> tag.

$vbulletin->GPC['message'] = preg_replace('/\[1d20\]/i','<img src="images/dices/dice_20_faced_'.mt_rand(1,20).'.jpg" alt="" />',$vbulletin->GPC['message']);

I'm running that code in newreply_post_start hook.