Theming image.html.twig
I'm not sure about overriding the &lt;img&gt; tag itself, but for your approach I would recommend overriding the field template. Assuming your field is named field_afbeeldingen, you can create a template called field--field-afbeeldingen.html.twig.

Within there, you could manually render your &lt;img&gt; tag as needed, with whatever additional classes required.