One surprisingly practical use I found for things like this; when internal tools throw up a 404 or a 503 with the usual default status page, people assume "oh it's not working, I'll try again later".<p>When they get an unexpected cat (or dog, in this case) they tend to go and ask their tech team, "what's with the cat?" It's not a substitute for good logging and alerting in any way, and is totally unsuitable for environments where internal tools need to appear professional and sensible, but as a way to get people to pay attention when something goes wrong then a cute animal can work a lot better than a "normal" notification.
Might be okay on a humour site, or perhaps in an internal tool, but some of these are a bit tasteless IMO. It could be far more useful if you were able to pick from a selection of individual images or image sets depending on the usecase. Although even then these kinds of http error images scream early-2000s web humour to me.
I've often wondered why most sites expose these status codes to the end user. The end user does not need to know, and in most cases will probably be confused by it. Plainly worded messages should be presented in the case of errors, not half an RFC.
At most early projects and cool clients, I'll throw together some goofy custom status pages for internal and sometimes public-facing websites and portals. BSOD, Chuck Norris quote generators, web games like Tetris, and so on.
It’s not a dog but still my favorite 404 is<p><a href="https://media4.giphy.com/media/6uGhT1O4sxpi8/200.gif" rel="nofollow">https://media4.giphy.com/media/6uGhT1O4sxpi8/200.gif</a>
Those are really cute!<p>You can optimize these a bit more using the Kraken.io web interface: <a href="https://kraken.io/web-interface" rel="nofollow">https://kraken.io/web-interface</a><p>Tried with a few and it shrinks them down ten to 20 percent savings without losing quality.