How to generate ID for image

When you add an image into a post it should have a class “wp-image-###” where ### is the image ID. Check the entire tag’s attributes, the class is not where one often expects it, it’s last on my installation.

Or maybe this occurs when adding to a widget? What widget are you adding images to?

The image is here https://spa.figa.lt/, it’s inside the post. I would like to set a css style for that particular image.

You used the media library to insert that image? Besides the usual ID class missing, the alignment class is missing as well. Either your theme or a plugin appears to be suppressing the class attribute output.

In any case, you can use the ‘get_image_tag_class’ filter to add/create/replace class attributes. The second parameter passed is the image ID, so this should be straight forward.

Since something appears to be suppressing class attributes, there’s a chance it could also suppress your effort as well. Adding your filter with a later priority (higher number) will hopefully bypass whatever else is going on.

When I press add media to post it doesn’t work. I found that this script is causing the error somehow, when I remove it the add media button works again:

var image_field;
jQuery(function($){
 //file upload
  $(document).on('click', 'input.select-img', function(evt){
    image_field = $(this).siblings('.img');
    tb_show('', 'media-upload.php?type=image&TB_iframe=true');
    return false;
  });
   window.send_to_editor = function(html) {
    imgurl = $('img', html).attr('src');
    image_field.val(imgurl);
    if(textarea.textarea=='') {
        textarea.textarea = '<img src="'+ imgurl + '"/>';
        $('.addhtml').val(textarea.textarea);
    }
    else {
        textarea.textarea=textarea.textarea + '<img src="'+ imgurl + '"/>';
	$('.addhtml').val(textarea.textarea);
    }
    tb_remove()
  }
});