<picture>
	<source media="(prefers-color-scheme: light)" srcset="https://placehold.it/180/ffff00/000000?text=Light%20image">
    <source media="(prefers-color-scheme: dark)" srcset="https://placehold.it/180/002244/ffffff?text=Dark%20image">
    <img src="https://placehold.it/180/ffff00/000000?text=Light%20image%20fallback" alt="" />
</picture>

<div>
	<button onclick="setPicturesThemed('light')">Set to 'light'</button>
	<button onclick="setPicturesThemed('dark')">Set to 'dark'</button>
</div>
/***************************************

Presentational styles for demo only!

***************************************/

body {
	display: flex;
	font-family: sans-serif;
}

img {
	display: block;
	width: 100%;
}

div {
	display: flex;
	flex-direction: column;
	margin-left: 15px;
}

button {
	margin-bottom: 5px;
	white-space: nowrap;
}
function setPicturesThemed(colorScheme = undefined) {
	document.querySelectorAll(`picture > source[media*="(prefers-color-scheme: ${colorScheme})"]`).forEach(el => {
		const cloned = el.cloneNode();
		cloned.removeAttribute('media');
		cloned.setAttribute('data-cloned-theme', colorScheme);
		el.parentNode.prepend(cloned);
	});
}

External CSS

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External JavaScript

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