Easy way to convert an image into AMP ?

If using the new AMP theme support, then you just output an img tag as you would do normally, and the plugin will convert it to an amp-img automatically. See https://github.com/Automattic/amp-wp/wiki/Adding-Theme-Support

Otherwise, you’ll need to take a similar approach suggested for adding ACF support to the legacy templates: https://github.com/Automattic/amp-wp/issues/440#issuecomment-399801866

Hello,

thank you. I made a quick and dirty function based on your answer

<?php	
/*
* AMPize : Convert html to AMP	
*/

function ampize($regular_html)
{
	
	$amp_content = new AMP_Content(
		$regular_html,
		amp_get_content_embed_handlers( get_post() ),
		amp_get_content_sanitizers( get_post() )
	);
	
	return $amp_content->get_amp_content();					
	
}

To me first answer convert every template and prevent my own amp template to work. I duplicated amp files in plugin folder to create my own template maybe that’s why.