Quick demo showing how to get a Base64-encoded
thumbnail.png file from a gist.
Thumbnails are very handy visual indicators of the content of a block on bl.ocks.org, esp for rapidly surveying a user's collection.
However, many block creators don't add thumbnails because of the extra steps involved in adding them to a gist. Since the gist API doesn't let you upload binaries you end up having to clone you're gist to add a thumbnail. Note: @mbostock's gist to clone all gists is useful here.
It's been suggested that the gist-img shell script enables you to upload thumbnail images. That's at least half true. It automates the base64 encoding of png images prior to upload with @defunkt's gist CLI tool, so you end up uploading the encoded text file.
In fact, it's easy enough to encode and upload such png files yourself:
base64 < thumbnail.png | gist -u 3883098 -f thumbnail.png.B64 -.
bl.ocks.org doesn't currently recognize Base64-encoded thumbnails.
FWIW, I opened up an issue for the
bl.ocks.org repo to see if @mbostock might enable (in all his copious free time!) the decoding of such thumbnails when rendering a block.