Using content from a perch:content id="" with PerchSystem::set_var

Hi,

I have a file that is accessed by every php file in a website:

<?php include($_SERVER['DOCUMENT_ROOT'].'/perch/runtime.php');?>
<?php set_include_path($_SERVER['DOCUMENT_ROOT']);?>
<?php preg_match('/MSIE (.*?);/',$_SERVER['HTTP_USER_AGENT'],$matches);
if(count($matches)<2){preg_match('/Trident\/\d{1,2}.\d{1,2};rv:([0-9]*)/',$_SERVER['HTTP_USER_AGENT'],$matches);}
$userAgent=isset($_SERVER['HTTP_USER_AGENT'])
?strtolower($_SERVER[$userAgent])
:'';
if(count($matches)>1){Header("Location:/unsupported/");}
?>
<?php header('Last-modified: . the_modified_date()');?>
<?php perch_layout('global.header',array('business_name'=>'Name of the Business'));?>
<?php
$url="https://".$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'];
PerchSystem::set_vars(array(
'googleid'=>'',
'fbappid'=>'',
'sitename'=>'Name of the Site',
'url'=>$url,
'heading3',perch_pages_title(true)
));
?>

which, denies IE among other things, that is later used:

<title><?php perch_layout_var('business_name');?> — <?php perch_pages_title();?> ‑ <?php perch_pages_navigation_text();?></title>
<meta charset="utf-8">
<?php perch_page_attributes(array('template'=>'default.html'));?>

and calls on a perch_page_attributes file (default.html):

<meta name="google-site-verification" content="<perch:pages id="googleid" type="hidden"/>">
<meta name="description" content="<perch:pages id="description" label="Description" type="textarea" escape="true" count="chars"/>">
<meta name="keywords" content="<perch:pages id="keywords" label="Keywords" type="textarea" escape="true" help="Separate with commas" count="chars"/>">
<meta property="fb:app_id" content="<perch:pages id="fbappid" type="hidden"/>">
<meta property="og:site_name" content="<perch:pages id="sitename" type="hidden"/>">
<meta property="og:url" content="<perch:pages id="url" type="hidden"/>">
<meta property="og:title" content="<perch:pages id="og_title" label="Social title" type="text" divider-before="Facebook Open Graph Tags"/>">
<meta property="og:description" content="<perch:pages id="og_description" label="Social description" type="textarea" escape="true"/>">
<meta property="og:image" content="">

however if there is an image on each page, I would like to be able to access this as per content="" using an id="" from a region in the current page (as per a .html template), e.g. for <meta property="og:image" content=""> so is this at all possible?

The .html template is:

<picture>
<source srcset="<perch:content id="webp" type="text" label="WebP image"/>" type="image/webp">
<img src="<perch:content id="jpeg" type="text" label="JPEG image"/>" alt="<perch:content type="text" id="alt" label="Alternate Text" help="Define alternate text for JPEG image"/>" class="<perch:content id="imageclass" type="select" label="Class" options="image_home,image_custom,image_custom1,image_custom2,image_about" help="Select image classname"/>">
</picture>
</template>

and I would like to be able to use the attribute value for the <img src=""> element. I am aware I can create a variable using PerchSystem::set_var() and use the assigned value in a .html template but I am hoping to be able to do the reverse.

Any help, as always is greatly appreciated.

P.S. I tried using <meta property="og:image" content="<perch:content id="_id1" type="hidden"/>"> to no avail so I'm not sure if what I am doing is wrong.