Force a thumbnail for the kirbytext image tag. Place this in /site/tags/image.php

image.php

<?php

// This file should reflect the image tag functionality found in /kirby/extensions/tags.php


// image tag
kirbytext::$tags['image'] = array(
	'attr' => array(
	'width',
	'height',
	'alt',
	'text',
	'title',
	'class',
	'imgclass',
	'linkclass',
	'caption',
	'link',
	'target',
	'rel'
	),
	'html' => function($tag) {

		$url     = $tag->attr('image');
		$alt     = $tag->attr('alt');
		$title   = $tag->attr('title');
		$link    = $tag->attr('link');
		$caption = $tag->attr('caption');
		$file    = $tag->file($url);

		// use the file url if available and otherwise the given url
		$url = $file ? $file->url() : url($url);

		// alt is just an alternative for text
		if($text = $tag->attr('text')) $alt = $text;

		// try to get the title from the image object and use it as alt text
		if($file) {

			if(empty($alt) and $file->alt() != '') {
				$alt = $file->alt();
			}

			if(empty($title) and $file->title() != '') {
				$title = $file->title();
			}


			// force a thumbnail
			$maxImageSize = c::get('maxImageSize', '1024');

			if( $tag->attr('width') and $tag->attr('height') ) {

				$url = thumb($file, array('width' => $tag->attr('width'), 'height' => $tag->attr('height'), 'crop' => true))->url();

			} else if(!empty($tag->attr('width')) or !empty($tag->attr('height'))){

				$url = thumb($file, array('width' => $tag->attr('width'), 'height' => $tag->attr('height')))->url();

			} else if($file->width() > $maxImageSize or $file->height() > $maxImageSize){

				$fit_to = $file->isLandscape() ? 'width' : 'height';

				$url = thumb($file, array($fit_to => $maxImageSize))->url();

			}

		}

		if(empty($alt)) $alt = pathinfo($url, PATHINFO_FILENAME);

		$image = html::img($url, array(
			'width'  => $tag->attr('width'),
			'height' => $tag->attr('height'),
			'class'  => $tag->attr('imgclass'),
			'title'  => html($title),
			'alt'    => html($alt)
		));

		if($tag->attr('link')) {

			// build the href for the link
			if($link == 'self') {
				$href = $url;
			} else if($file and $link == $file->filename()) {
				$href = $file->url();
			} else {
				$href = $link;
			}

			$image = html::a(url($href), $image, array(
				'rel'    => $tag->attr('rel'),
				'class'  => $tag->attr('linkclass'),
				'title'  => html($tag->attr('title')),
				'target' => $tag->target()
			));

		}

		$figure = new Brick('figure');
		$figure->addClass($tag->attr('class'));
		$figure->append($image);

		if(!empty($caption)) {
			$figure->append('<figcaption>' . html($caption) . '</figcaption>');
		}

		return $figure;

	}
);