No there is no B2evo trick. This is simple XHTML.

<div class="recaptcha">your code goes here</div>

and some stylesheet:

.recapthcha {
    margin-left: auto;
    margin-right: auto;
}

The <center> tag is deprecated and replaced by

text-align: center;

however that will only center inline elements. An image is a block element.

In your situation it's easiest to use some existing class that already centers images. That saves you adding the extra css/stylesheet.

Good luck

as a follow-up, can I provide and access that stylesheet from within the plug-in, or do I have to instruct users to modify their skin's stylesheets?

Usually a plugin ( that requires styles ) ships with it's own stylesheet and adds it to a skin like this :

	/**
	 * Spits out the styles used
	 *
	 * @see Plugin::SkinBeginHtmlHead()
	 */
	function SkinBeginHtmlHead()
	{
		require_css( $this->get_plugin_url().'style.css', true );
	}

¥

Ok, I'm still not getting it!

I read the docs for [url=http://doc.b2evolution.net/HEAD/evocore/_blogs---inc---_core---_template.funcs.php.html#functionrequire_css]require_css()[/url] and the code within [url=http://doc.b2evolution.net/HEAD/__filesource/fsource_evocore__blogsinc_core_template.funcs.php.html#a520]_template.funcs.php[/url] and this is supposed to output a stylesheet link, ie.

<link rel="stylesheet" href="templates/subSilver/subSilver.css" type="text/css"/>

I added the function Yabba provided above, but when I saved the file, refreshed the page and viewed the page source, I didn't see my stylesheet link (recaptcha.css).

I looked at the creativecommons_plugin code, because that stylesheet is printed in the source of the page, and the author of that plugin manually provided the stylesheet link:

function SkinBeginHtmlHead() {
        echo "\n".'<link rel="stylesheet" type="text/css" href="'.$this->get_plugin_url().'cclicense.css" />'."\n";
        }

I tried this method, but did not get the same results. How can I debug this process to determine why my code is apparently not being executed?

Thanks.

A quick follow-up:

Out of desperation, I went into the backoffice, disabled my plugin and then re-enabled it. After this, I refreshed the page and the stylesheet link was there!

Hopefully this bit of knowledge will save someone some frustration and time in the future!

Sorry, I forgot to say that when you add new hooks to a plugin you need to goto admin > global settings > plugin install and click "reload plugins"

The require_css() method is the most future proof ;)

¥