rucativava

Didn’t work for me. This is my output:
<meta property="og:description" content="… <a href="https://www.aaaaa.com/jjjjjj/lllllll/" class="read_more">[read more]</a>" />

Just to let you know that, not finding any other information, I followed your advice successfully.
I used this https://codex.www.ads-software.com/Plugin_API/Filter_Reference/the_content and this
https://php.net/manual/en/ref.strings.php .
Maybe I might as well paste the code I wrote here, in case somebody stumbles upon this post and gets curious about my smudgy bites:

function modify_capa($content) {
 	if(in_array('get_the_excerpt', $GLOBALS['wp_current_filter'])) return $content;
	if (strpos($content,'alt="capa"')): ?>
		<?php

			// FIND CAPA
			$capapos = stripos($content,'capa');
			$imgend = strpos($content,'>',$capapos);
			$imgend = $imgend;
			$content_length = strlen($content);
			$imgend_fromend = -1*($content_length - $imgend);
			$imgstart = strrpos($content,'<',$imgend_fromend);
			$img_length = $imgend - $imgstart+1;
			$capa_img_tag = substr($content, $imgstart, $img_length);

			//FIND ATTACHMENT ID
			$id_start = strpos($capa_img_tag,'wp-image');
			$id_end = strpos($capa_img_tag,' ',$id_start);
			$id_string = substr($capa_img_tag, $id_start,$id_end-$id_start);
			$capa_id = substr($id_string,strrpos($id_string, '-',-1)+1);

			$capa = wp_get_attachment_image_src( $capa_id,'publication');
			$new_capa = '<img class="capa-shadow" src="'.$capa[0].'" alt="capa" width="'.$capa[1].'" height="'.$capa[2].'" />';
			echo $new_capa;
		?>

		<?php //INSERT NEW CODE ?>
<div> HTML stuff <?php echo 'with php stuff'; ?> </div>

		<?php 

		//REMOVE OLD CAPA
		$content = str_ireplace($capa_img_tag,'',$content);

	endif;

	return $content;

}

add_filter( 'the_content', 'modify_capa' );

Raby:

I think we’re on the right track. That is what I want. Some kind of function that will override what is written in the post. From what I understand, your code will override any image dimensions with the given ‘SIZE_YOU_WANT’ dimensions.
Do you know how can I limit this update_option() to a specific part of my .php file? e.g.: single.php main loop.

I am using WordPress as a CMS for this project. Posts will work as containers of information on specific products. My client needs to alternate some images with text – the post editor is perfect for this; but I want to override possible mistakes made by him regarding chosen image size. That is why I need to override the output image_size with the one I already created through add_image_size(‘post-width’,750,500).

I want to use the wordpress crunched images because it is the most optimized way in terms of size (kb). Javascript and CSS might present two problems:
1 – If the given image in the_content() is smaller, I’ll get a blurred bigger one.
2 – If the given image in the_content() is bigger, I’ll waste bandwidth and memory.
Since WordPress is a CMS that handles resizing images, isn’t it normal to be able to use these kind of functionality?

That is a real pitty, that you cannot manipulate the content of the_content(). Neither with filters or such?

Thank you for the link. I’ve been there already, and I’ve been using these add_image_size() thoroughly in my template when I know the ID of the attachment.

What I need to know is how to make all images in a post be output with a specific image size in the course of the_content().

That is one way, the wrong one in my opinion.
I want it to happen server side, while wp renders the page, and uses its crunched images in the add_image_size() i created in funtions.php .

Yes, please.

Unsal,
Thank you for adding this functionality. So the way to adjust sharpening is through tinkering those 3 numbers? Is there a way to choose a number in a 0-10 scale?