I made a little example project a few years back. The format is dead simple, keep the connection open, flush multiple JPEGS separated by a header. It's used pretty often by cheap security cameras and is supported by most browsers. It just seems to be not widely known about.
The demo is still live:
Gmail still allows marketers to track when a user opens an email (even better than before, since it no longer asks users whether they want to load images). However, they proxy the request so that the tracking pixel host no longer gets the user's IP address or third party cookies.
The change is that clicking to load images is no longer the default 
Do you get enough spam on your Gmail for this to be a worry point? Genuinely curious; I get roughly zero.
Eh? Before they used track-me.example.com/IDHERE and got blocked, now they use IDHERE.track-me.example.com and don't get blocked.
Move the unique ID to DNS and Google will let it through.
Yes if you load images they can track that you have opened the email.
I fail to see how that is 'unsafe' though. It's expected functionality.
(That, and you can cache-bust on a per user basis using a unique identifier in the query string.)
You'll see that it in fact does get cached by Gmail, but only for a limited time.
If I send you an image URL http://example.com/fH27cAw, and they URL is requested, you must have opened my email (unless something is requesting them regardless).
(All-caps three character properties, namespaced(?) arguments, spaces e v e r y w h e r e, curly bracket array access.)
Also, I didn't know `class` and `array` were case-insensitive.
Some of what you mentioned is already present there. Some other things are new. But they're both terrifying...
Extra details: the rewrite into gifencoder happened in 2007, so gifmerge must be older than that (maybe 4.x times). The original license forbids modifying gifmerge without author's approval - since this file doesn't mention it at all, I doubt dmimage is legal.
Welcome to PHP! Truly the language which most directly represents the soul of the web - a stateless static documentation presentation system which we shoehorn application functionality into regardless of the pain!
I used to agree, but more recently have decided it ultimately ends up making things more difficult to read by increasing the amount of scanning your eyes need to do.
> what about progress bars for stuff that your server is doing in the background
This seems like a really good micro-service.
A bit later, web browsers cleaned up their implementations, and it no longer works.
Good times, though.
I wonder if it would be possible to make a live WebM version of this instead.
 IOCCC 2013 winner, most timely rendered: http://www.ioccc.org/2013/mills/
Nice to see the forgotten technology repurposed.
Looking at the git commit history, this was created ~2 days ago.
And instead of being snarky, you could actually explain what is so novel about dynamic image generation on a server.
This is generating a custom GIF file on the server. It's most likely been done by someone somewhere before, but not something I've been both gaming and forum-ing for a little while.
I have not seen a generated GIF before.
The watch on the home-page displayed the current time with moving hands that were behind reflective glass. It was a server rendered gif. (c) 1996 or '97.
 http://roxen.com - now an Enterprise / Newsroom CMS.