There is now an option to prevent animated images, like GIFs, from playing automatically. By default, GitHub respects your system level preference to reduce motion. However, you can also disable autoplay entirely in the Accessibility settings. Once disabled, two buttons will let you control animated images: a play/pause button, and a button to open the link of an image.
You can now specify whether to display images for light or dark themes in Markdown, using the HTML <picture>
element in combination with the prefers-color-scheme
media feature.
For example:
<picture>
<source media="(prefers-color-scheme: dark)" srcset="https://user-images.githubusercontent.com/25423296/163456776-7f95b81a-f1ed-45f7-b7ab-8fa810d529fa.png">
<img alt="Shows an illustrated sun in light color mode and a moon with stars in dark color mode." src="https://user-images.githubusercontent.com/25423296/163456779-a8556205-d0a5-45e2-ac17-42d089e3c3f8.png">
</picture>