[jstarfish]

Specifically for a gallery page of search results, I'd guess that it's to provide a more-consistent experience.

When you load that results page, you'd be reaching out to ~100+ different domains that will respond and render the images at different rates (and some will fail to load at all). Base64-encoding lets you shove binary content into caches like Redis, retrieval and embedding of which would be preferable to hotlinking to a slow site. Then most of the page gets rendered at the same time client-side.