Blazy for hard-coded image, non-media entity

> image hard-coded into a theme
If you could place your code, I might be able to help better?

However, hard-coded or not, Blazy works perfectly fine with dead or archived HTML, twig, and PHP. It started with dead HTML, anyway.
To get a better idea on how Blazy works, try viewing the existing Blazy formatter output, CTRL/CMD + U.

The following should give you a big picture in TWIG usages.

See blazy.libraries.yml for more advanced usages:
{{ attach_library('blazy/load') }}
{{ attach_library('blazy/ratio') }}

The SVG placeholder is better than gif, but just longer and uglier:
{% set placeholder = "data:image/svg+xml;charset=utf-8,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20viewBox%3D'0%200%201%201'%2F%3E" %}

{% set url = 'https://www.drupal.org/files/One.gif' %}
{%
  set attributes = create_attribute({
    'data-src': url,
    'src': placeholder,
    'loading': 'lazy',
    'class': ['media__element', 'b-lazy'],
    'width': 640,
    'height': 360,
    'alt': 'Preview',
  })
%}

For more aspect ratio, see <em>css/components/blazy.ratio.css</em>
<div class="media media--ratio media--ratio--169">
  <img{{ attributes }}/>
</div>

Or the simplest, but needs more theming to avoid collapsed images, etc:

{{ attach_library('blazy/load') }}
<img data-src="{{ url }}" src="{{ placeholder }}" alt="{{ 'Preview'|t }}" class="b-lazy" loading="lazy" width="640" height="360" />

placeholder can be:

'/blank.svg'
'/blank.gif'
'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7'
"data:image/svg+xml;charset=utf-8,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20viewBox%3D'0%200%201%201'%2F%3E"

The first two hit your server with HTTP requests, bad but can be handy from within Views results as noted at project home.
The last (data URI) won't, normal Blazy usages.
For dynamic/ field image urls, use core function here https://www.drupal.org/node/2486991#s-file-urluri → , or twig_tweak module for more functionality.

Pro tip:
Don't be fooled by Console Inspector (F12), use its Network tabs to verify the lazy load workflow.

Updated attributes to img_attributes in case copied as is and conflicting with normal theme reserved attributes.

Feel free to share your findings.

Thank you.

Automatically closed - issue fixed for 2 weeks with no activity.