This is (yet) another thing I always forget how to do…
<img alt="Red Square" src="data:image/png,%89PNG%0D%0A [...elided...] %60%82" />
With a compatible brower, this gives:
Doesn’t necessarily work with all browsers (so you know what to do if you can’t see a reddish-brown square), but it can come in handy at times.
As always, Wikipedia has the lowdown on the whole “Data URI” thing…
