Edit Options - Block NSFW Images

[ShatterStudios]

So, I'm trying to add this functionality to my site, and I can't quite get it working.

I put a field in the Edit Options page in the User CP with a checkbox to block NSFW images posted with an alternate BB code. Then I made a BB code to look for a variable that the checkbox in the Edit Options page sets, and if the option was enabled, it would post a standard image instead of what the person originally posted that just said, "NSFW" (I installed this hack, Advanced BBCode, which is supposed to allow conditionals in custom BB codes).

Problem is, I don't know how to code (which would also account for any of what I'm saying not making sense to you). What I did was copy/paste the code for the invisible option and replaced all the labels and IDs and such. When I test it out, the checkbox doesn't stay checked. Not sure if the BB code I made will work, but I need to figure out the options field first. The code on the Edit Options page looks like this -

<fieldset class="fieldset">
	<legend><label for="cb_nsfw">Block NSFW Images</label></legend>
	<table cellpadding="0" cellspacing="$stylevar[formspacer]" border="0" width="100%">
	<tr>
		<td>This will block any images tagged as not suitable for work, so you can safely browse the site in the presence of your boss, your family, or whoever.
		</td>
	</tr>
	<tr>
		<td><label for="cb_nsfw"><input type="checkbox" name="options[nsfw]" value="1" id="cb_nsfw" $checked[nsfw] />Block NSFW Images</label><input type="hidden" name="set_options[nsfw]" value="1" />
		</td>
	</tr>
	</table>
</fieldset>

And the replacement for the new BB code (named NSFW) looks like this -

<if condition="$userinfo['nsfw']"><img src="http://www.nsfw.us/nsfw_logo.gif">
<else /><img src="{param}">
</if>

What do I need to do to make the checkbox stay checked and have something for the BB code to look for? Do I have to declare cb_nsfw somewhere, or what? I really have no idea where to go from here, so any help would be greatly appreciated.