Custom BB code translated by plug-in

[ShayA]

How do I add a custom BB code that will be translated by a plug-in:

I will define a new custom BB code, name it as [PHOTO].
Suppose that in the editor I will write [PHOTO]http://www.123.com/p.php?if=100[/PHOTO]

I would like to have a plug-in that will be run for every [PHOTO] BB code. That plug-in will get the [PHOTO] BB code staring value and will return a string that will be placed instead.

How this can be done.

Thanks,