[Viper007Bond]

e) Not possible without using PHP to download the image file and then examine it with some image functions from the GD module.

As for the rest, something like this would probably do I think:

PHP Code:

$text = preg_replace('#\[yourtag\]http://([A-Za-z/.]+)\.(jpg|gif|png)\[/yourtag\]#si', '<img src="http://$1.$2" alt="" />', $text);